okay, so a few things
1) you're not getting laid at this event. *might* be different if it's an unofficial/house party type situation, but even then doubtful, basically nobody goes to actual school events looking to get laid
2) seriously, it's just not gonna happen, you'll be better off if you accept it
3) even if it WERE possible, the fact that "getting pussy" is equated with "having a good time" in your mind means it's DEFINITELY not going to happen. the fact that you're posting for advice on a fitness subsection of an anime forum means you're definitely not a natural at this sort of thing, and if you go out for the purposes of getting laid it's gonna show, and you're gonna come off as creepy and weird
4) by setting "getting laid" as your goal, you're turning an opportunity for fun and relaxation into a challenge, one that you don't have complete control over.
5) you're at your most attractive when you're relaxed, confident, and fun. you're naturally like this when you're at a party for the sole purpose of having a good time, because you're in complete control of your success. if you're not having fun with some girl, then fuck it, who cares if she's super hot, go actually have fun with someone else. it's slightly paradoxical, but i promise you, every time i've had a one night stand at a party i was 100% not planning on it and just looking for a good time. because...
6) when you're going out to get laid, you're going to automatically be more self-conscious, nervous, and on-edge. the longer the night goes on, and the lower your chances become, the worse you're gonna get. when you approach girls, it'll be with an ulterior motive lurking in the back of your mind, and even if it's only on a subconscious level they're gonna be able to tell
7) this is a perfect opportunity to make some friends. go there with *that* on your mind. have fun, and make friends. don't even think about getting laid. i promise you'll be better off for it