today

Today was the sports festival in at our high school.
It was very hot and I'm tired.However, we were excited., and enjoyed it very much.
We were divided into three groups: "紅蓮," "黄神," and "青龍".
I belonged to was in "黄神," and our group won!!
I felt the friendship.
I am a senior., so next year, I can't participate in the sport festival.
In the evening we went to dinner together.
The restaurant was full of our high school students.
After that, only six people including me went to karaoke.
Today I was happy!!

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Your english is very good! the only problem you had was with punctuation.

I know when you say you're in a group in japanese, your basically saying, "I belonge to [group name]." But that sounds weird in english. It would be better to say, "I'm in [group name]."

Another common mistake with japanese people learning english is mixing up "at" and "in". Just remember "in" basically means "中", and "at" is more like "で".

Your english is way better than my japanese! :P
頑張れよー！