"Afraid" of social situations?

It's not exactly a fear I would say, but I do feel somewhat afraid of the idea of going someplace, say a party, where there will more than a couple people I don't know. I just feel like the people who I don't know, regardless of the fact if I will even have to interact with them, won't like me, and that the people I do know will leave and go hang out with them or something like that. Being in high school, not wanting to go to a party is a terrible thing. How can I get over this fear?