How to get to know this girl better without seeming like a creep?

So this girl was in my drivers ed class and after it was over I sent her a friend request on fb. She accepted but now I don't know how to get to know her better. There's a fair in my town right now and she's gonna go there today. I saw her there yesterday and said hi but then freaked out and left really fast. I have social anxiety so I get freaked out around crowds of people. I really want to at least get her number, just so I feel like I accomplished something. But the problem is, she has a LOT of friends and always hangs out with them. I get intimidated when talking to a group because I feel like they're gonna be judging me and everything I do. I'd feel much more comfortable talking to her alone but there's no way that will happen. So I was wondering how can I get to know her better without making it awkward. She's really nice but I don't want to seem like a stalker or something. So when I see her, how do I get her number. It would be rude to just ask for it and leave, but It would be too awkward to hang out with her when she doesn't even know me. We don't even go to the same school. And plus she already has her group of friends she hangs out with, and I'm kind of a loner because of my anxiety. So how can I come up to her again today and ask for her number without her thinking I'm a stalker or creep? PLEASE help. I'll be so depressed if I chicken out again, but I don't want to be too annoying either.