What should I do with my classmate?

So there is a girl that is in same class with me for like 2 years and we were on a birthday party, get couple of drinks, danced but not kissed. After a week or so i ask her out and I took my friend and one her friend. I got c*ckblocked by that f*cker twice and since then I didn't really talked with her too much, but I still liked her. Now it's our graduation and I asked her to be my prom and without thinking she said yes (before me she refused one guy). Now we are cool but I am not sure if she likes me, cause i really do. I can see her sometimes staring at me but when i talk to her i don't get that flirting, she's kinda cold like nothing happens.
Now I really dont know what to do... If I tell her now that I like her and she refuses that would ruin our prom, cause the party is like for a month.

Please give some advises :/

When there is chemistry you feel it. She may be interested in you, but if there is lack of chemistry she is going to get bored eventually. When you say you got cocked blocked, why is it that it's hurting your feelings that someone else is flirting with her. Aren't you confident enough to know you are unique, and what you bring to the table is unlike any other guy out there? You should of been yourself even if there was a cock block. If he was being rude to you, you act like a normal human being and tell him you don't appreciate the way he's acting.

I don't see the need to tell her that you like her. It's the chemistry that matters. When there is chemistry there is no need to tell someone you like them, it just feels right for both of you to move things to the next level.

Rather than telling her that you like her, why don't you ask her if she wants to grab an ice cream with you after school or something? Invite her to the movies also... so you can get to know each other better and see if there's chemistry or not. Up till now, you two are basically still strangers. Also, if she doesn't accept your invitation, you'll know that she doesn't like you and you won't be anxious to find out anymore. It's a win-win.

I agree you should spend time with her getting to know her, instead of assuming you like her....you really don't know until you get to know them away from school and friends. Everyone acts differently when not surrounded by other influences. Don't get too eager, be cool, and relaxed, don't force things.....let her try to figure what you are all about. If you get all sappy and clingy, you will fail.