I can speak as someone who thought they couldn't do parties. Parties are incredibly intense, and can be the best or worst experience of your life depending on the smallest details. Eventually you will learn how to party best for you, what substances to take, what to wear, where to stand and what to do, which parties are just not going to work for you. Keep trying new things, but also if you're not feeling it, take some time out or just leave.
I think the older you get, the more you realize that everyone has imposter syndrome and anxiety all the time, but you just have to fake it until you make it. If you pretend everything is fine, it usually turns out fine.