Good thing, Sunshine30 is an expert of these situations.
So first of all, I'm going to resolve your first point "people are going to get drunk and stuff i think
and i puzzled"
Remy's answer: Actually it's a party so normally people are going to be drunk but no worries at all, you don't want to drink you don't. You can drink one glass or two but not more if you don't feel too. If you don't feel comfortable with these people then go away. Don't be shocked by what you will see.
Secondly "if i do get drunk or hiper and just snog someone else i have a boyfriend and all AND Im SCARD"
Remy's answer: The probability of having a **** when you are drunk are very low, it doesn't happen everytime you are. You have to be very drunk if you snog someone and more. But if it happens, no worries, you are drunk, we were in an other world, you can be forgiven, I know what I'm talking about.
Conclusion: Apparently you haven't the habit to go to a party so let's relaw, find some friend you get along with, don't drunk if you don't want to and everything will be alright. You will have fun of course !