(This is how someone speaking US English would say this.)   My first experiences at college.

Hi! My name is Maria Alejandra.  I'm from Colombia, and I am going to tell you about my first experiences at college. 
First of all, I`m from a small city, so when I passed my college entrance exams (to study petroleum engineering ), I was so excited about this new opportunity and the chance to get to know people of different cultures.  This was the most important decision that I had made in my short life!  My parents and sister were so proud,  and all my friends were so happy for me.
The first day I arrived in  this big city, I was in shock; THIS CITY WAS SO MUCH BIGGER!....wooooah, I don`t know how to explain the sensation, the feelings of apprehension, happiness and nervousness.
My first day at college was so strange,[ nothing that i think of this was real]  (I don't understand what you mean here)  it was like I was in a dream (?).   The thing that was great about it was that I already had some friends in other departments,  which was great because all of us are so different (different clothes, different accents,  and our opinions and customs are sooo different)
Now I am learning, accepting and living a unique experience, and day after day this is most amazing (You could also say, ..".this is really amazing" ( "This is most amazing" sounds really formal)....so wish me luck!
Bye