I had an us student visa interview.  On Monday, I travelled to Seoul to interview for a U.S. student visa.

I went to Seoul to have a us student visa interview from monday to Tuesday.

I was a bit nervous cuz a person who was in front of me looked very worried.  I was nervous because the person, that was in front of me, appeared to be very worried.  

Fortunately, the interviewer could speak Korean so I though he is Korean at first, but I could tell he is not a Korean because of his accent. Fortunately, the interview could speak in Korean, which gave me the first impression that he was Korean.  However, I could tell that he was not, due to his accent.

He asked me how long am I going to stay in the us? The first question he asked was, "How long are you going to stay in the U.S.?
I answered 'four months' he said according to the 'I-20', it says twelve month. so I said it's at least four months to the longest, twelve months. So he passed me and said the visa papers that I submitted will be sent to my home within one week.

My answer was, "Four months!".  He, then, said that according to the I-20; it says "twelve months.".  He stated that I could stay up to a period of twelve months.  He passed my application and informed me that my visa papers will be sent to my home within one week.

Do not start a sentence with "so."

After the interview, I went to YBM n Pagoda language school, which is popular in this industry. I had a level test for the conversation class with a native teacher. He was from Winnipeg, Canada, which my friend immigrated to.   After the interview, I went to YBM and Pagoda Language school, a popular school in this industry.  I took a level test for the English conversation class with a native-speaking teacher.  He happened to be from Winnipeg, Canada; the same place my friend emmigrated, from Korea, to.  The word is "emmigrated", not "immigrated".  "Emmigrated" means that your friend travelled from Korea to Canada.
He evaluated my English level 5+ grade out of 6 grades. The teacher evaluated my English-speaking level as a '5 out of 6'.

I was a bit sad, that my English level is still not the highest level even though I studied English in Canada for six minths.   It made me somewhat sad that my English level was not at the highest grade, despite the fact that I had studied English in Canada for six months.
I hope my English would be perfect after I finish my study in the US.  It is my hope that my English will be better upon finishing my studies in the U.S.

I had an a ('a' because the sound of 'u' is you) US student visa interview

I went to Seoul to have a USA student visa interview lasting from Monday to Tuesday.

I was a bit nervous cuz a because the person who was in front of me looked very worried.

Fortunately, the interviewer could speak Korean, so I thought he is Korean at first, but soon I could tell he is not a Korean because of his accent.

He asked me how long am I going to stay in the US?
I answered 'four months'; he said according to the 'I-20', it says twelve month. so I said it's at least four months to and the longest will be twelve months. So he passed me and said the visa papers that I submitted will be sent to my home within one week.

After the interview, I went to YBM n Pagoda language school, which is popular in this industry. I had a level test for the conversation class with a native teacher. He was from Winnipeg, Canada, which my friend imemigrated to.
He evaluated my English level at 5+ grade out of 6 grades.

I was a bit sad, that my English level is still not the highest level even though I studied English in Canada for six months.
I hope my English would will be perfect after I finish my study in the US (unlikely! but better!)

I had an US student visa interview

I went to Seoul to have a US student visa interview from monday to Tuesday.

I was a bit nervous cause (because -> cause) the (because you're talking about a specific person, you use 'the') person who was in front of me looked very worried.

Fortunately, the interviewer could speak Korean, so I thought he was Korean at first, but I could tell he is not a Korean because of his accent. (It would be more natural to say "Fortunately the interviewer could speak Korean. I thought the interviewer was Korean at first, but I knew he wasn't because of his accent.")

He asked me how long I was planning on staying in the US?
I answered 'four months.' He said according to the 'I-20,' (punctuation goes inside quotations!) it says twelve months. So I said it's at least four months or to the longest: twelve months. So he passed me and said the visa papers that I submitted will be sent to my home within one week.

After the interview, I went to YBM n(and?) Pagoda language school, which is popular in this industry. I had a level test for the conversation class with a native teacher. He was from Winnipeg, Canada, where my friend immigrated to.
He evaluated my English level 5+ grade out of 6 grades.

I was a bit sad, that my English level is still not the highest level even though I studied English in Canada for six months.
I hope my English will be perfect after I finish my study in the US.

I had an US student visa interview

I went to Seoul to have a US student visa interview from Monday to Tuesday.

I was a bit nervous because a person who was in front of me looked very worried.

Fortunately, the interviewer could speak Korean, so I thought that he was Korean at first, but I could tell he was s not a Korean because of his accent.

He asked me how long was I going to stay in the us?  (If you were quoting speech, you could say am I otherwise was I)
I answered 'four months' he said according to the 'I-20', it says twelve month. so I said it's at least four months to the longest, twelve months. So he passed me and said the visa papers that I submitted will be sent to my home within one week.

After the interview, I went to YBM n Pagoda language school, which is popular in this industry country?. I had a level test for the conversation class with a native teacher. He was from Winnipeg, Canada, which my friend immigrated to.
He evaluated my English level 5+ grade out of 6 grades.

I was a bit sad, that my English level is still not the highest level even though I studied English in Canada for six minths.
I hope my English would will be perfect after I finish my study in the US