Should I apologise to her, or leave her alone? Please help!?

Leave her alone. Though it may be hard, it's for the best, and it'll spare you a lot of confusion. If she wants to talk to you, she will, no matter how shy she is. But right now she may feel awkward because it seems you came on a bit strong. Don't beat yourself up about it though. You'll only upset her more by trying to apologize. Just let things play out, and she'll forget what happened, and maybe you can have a fresh start.