I like a girl, she thinks I'm creepy.

I just want to get to know her, but I get nervous around her. She laughs at my jokes, but that's not saying much since the whole class laughs at them. The nervousness's probably because of an occurrence in freshman year.

Some problems: She's a close friend of my ex-girlfriend and they've been friends for like three or four years. A guy friend of mine told her I liked her (one of my close friends told him it as a joke, only those two know I like her), she supposedly said "That's creepy" (the friend that told her is really sarcastic and lies a lot). One of my best-friends used to like her on and off for four years, but he's okay with me liking her since he thinks he's too awkward to tell her and he doesn't really try to talk to her.

How do I get over my nervousness so I can talk to her? We have gym/health together, but she sits with her best-friends all the way in the back of class, while I sit in the front with a bunch of my bros, we're friends on Facebook.

I asked her to Homecoming. She couldn't go cause she was going to a Duke football game with her dad and friend. I took so long to ask her because of my best-friend, I didn't want to hurt his feelings, but everyone else told me to just ask her. And now, I've pretty much confirmed that I like her since I asked her.

How do I talk to her more often without getting nervous? I'm generally a confident guy, just not around her. I guess it's mostly because she said I was creepy last year when my friend told her I liked her and because she pretty much rejected me for Homecoming, in addition to her being extremely attractive.
We talk like once every three weeks, usually on Facebook. She sits on the opposite side of the health class and she always hangs out with her good girl-friends during gym. I only see her in the halls after health/gym class. No other time, really, since she's always on the other side of the school in a long hallway. The only classrooms there are the two art classrooms, so I have no excuse to go over there to talk to her since it's obvious that I don't take art.

Normal ways to getting over nervousness don't help me. And health/gym class has no homework, so I can't talk to her about homework. Every once in a while, she needs help with Chemistry labs and concepts, so she chats me on Facebook and I help her with that every few weeks. That's pretty much the only time we communicate.

And regarding her thinking that I'm creepy. So when I asked her to Homecoming, we just had gym class and I was talking to a friend in the cafeteria before I went to my next class. Then I see that she's coming into the cafeteria and so I walk towards her since it was on my way to my next class. I ask her in a mini-hallway leading to the cafeteria and as you know, she couldn't go and obviously didn't want to. She apparently told the other soccer girls that I waited for her to leave the girl's locker room and asked her in front of the girl's locker room, which expressed her view of me being creepy. I'm thinking of just not doing anything anymore because I don't want to make her uncomfortable if she really thinks I'm that creepy.
I also don't want to come off as arrogant, but I'm one of the "well-known"/"popular" guys and so, some friends told me to continue chasing her because I'm not actually creepy, but she just doesn't know me well enough, so she said that. However, I disregarded what my friends said.

She apparently "likes" a guy (the guy is known to be pretty creepy and a pervert, so many think she's lying) and my best-friends are trying to get her to talk to the best-friend that also likes her. My friend who's her close friend told me that there's a high chance that she'd think I was more creepy if I talked to her. I have no idea what to do and I'm thinking about giving up.

Well, thanks for taking the time to read and your advice is very much appreciated!