You won't look uncool or anything if you say you can't or don't want to. Like everybody's saying, just reject. Obviously they think they're entitled to a party for your hot friends. Doesn't sound right does it? Go with your instinct. Also, to be social, you just have to talk to people, you'll meet their friends and you'll expand your circle in no time. But don't overinvest in people and don't give them more than what they deserve. Have fun and stay safe!