Woah, if you didn't hit on her the first time she locked eyes with you then you have blown your chances?
Golddust I completely disagree with that, if that was true the majority of pretty ALL men who have girlfriends would be single now.
Attraction isn't so black and white dude, sometimes it happens from word go but most of the time real genuine attraction builds over time especially when we are talking about high school where girls haven't become shrewd from years of failed romances yet and still compare most of the guys they meet with Edward Cullen.
S Wild I sincerely doubt she has pigeon holed you as a shy loser because you didn't jump her the first time you made eyes with her.
If you're interested in her then go talk to her, don't neg her, don't DHV, don't put on a fluffy purple hat, just introduce yourself and ask her about her interests, her passions, how many pets she has, whatever feels most natural in keeping a conversation going and don't over think it either just say what is on your mind.
And read this
http://wayoftheplayer.com/the-best-of-w ... proaching/ it will help you A LOT.