Have you joined any clubs? I found I met a ton of people outside of first year by doing that. I'm not someone who makes friends super easily, but I found my small group of 2-3 people I spend a lot of time with, and I know of at least 7-10 I can meaningfully chat with between classes or at events.
As far as the girls who have been mean already, I've found the cliquey mean girls exist in every life stage, no matter how far from high school you get. In a strange way, it's helpful they showed you their true colors now so you don't waste your time on them (not that that makes it hurt less, I don't want to invalidate that). It's 100% a them problem and not a you problem.
I also frequently feel as if I'm not "socially successful" because I don't have a big group that goes out on the weekends and has fun, but I have my people, and I tend to hold those people close. It's okay if that's how you are too. You don't need a group of 12-15 people to have good friends.
Is that rambling or too many cliches? I don't know. This is your first year and people are still finding their place and their footing. I would have told you up until about February of first year that I didn't feel like I had friends at school, but those relationships were just taking some time to build. All of you have been through a massive life change and taking your time to settle in is okay. You'll find your place, it might just take a bit longer than you hope.