Sounds like you're in HS? Thing is, HS is one big popularity contest. So, approaching this like some normal outside interaction AKA let's hang out sometime isn't the best approach. Not bad, but less effective in this particular setting.
First, good for you for being proactive and asking her out in the first place, because at least that shows her you are a man that goes after what he likes. Now, don't change anything you're doing in particular...be the same guy you been, but don't go out of your way to ask her out again; only if you spot a hint that she's giving (e.g. "I'm free this weekend," "I would really like to go see this [movie]," "I'm bored I wish I had something to do.") Anything like that, go ahead and ask again.
On the other hand, if you can start making good with some girls around the hall, or maybe even some of her friends, you can bet your ass that's going to pull her heartstrings into gear. The moment she recognizes that she may lose an opportunity to hang out with you, and she sees her friends taking interest in you, she's going to be purring up right next to you, tail in the air.
So, I would suggest you do that. Go make friends with her friends. A simple, "Hey, you're [girls] friend right? She's so funny in our class.. Nice shoes by the way." Just a simple line about how you're connected and low-level compliment will make them feel good. Something like that is so easy to get them on your good side, and then casually keep saying hello as the days go on and build relationships!
The surprise is that at the end, you may not even be thinking about this girl anymore when you got the attention of other girls too...