-I like how you made this into a letter format
I am so happy to meet you since I miss so much my three ex-roommates of my high school dormitory.
--> I think you should re-write this sentence. I think you are trying to say something about how you miss having roommates (because you experienced this before) and you are glad to have a roommate once again! Your sentence right now is grammatically incorrect...
If you want to know about me
characteristics hidden in my stuff.
-->..hidden in my belongings.
-You can make this sentence more clear by saying that the things you possess are representative of some of your personality traits. It doesn't really make sense to say that characteristics are "hidden" in your stuff...
I am so excited to show you this essay at the dormroom.
--> I think you should cross this sentence out.
-Overall, I think this is a very bright/happy essay.
-I guess this essay does answer the prompt, but I was thinking more about revealing something about who you are as a person opposed to something you are good at like a talent or something.
Good Luck : )