New here, looking for some advice.

2 days ago, I was on a high because I finally overcame my approach anxiety and walked up to an attractive girl whom I'd never met before in one of my classes. As I was speaking to her and scrambling for words, I stupidly suggested that we should swap numbers so that we can help each other out on future homeworks, instead of making my intentions more direct. She was really nice about it and gave it to me. Fast forward to today where I again have class with her. I come in a bit late and see that there aren't any free seats next to her. "No worries, I think to myself. I'll talk to her when class ends." So class ends and as she's walking towards the exit, I start walking towards her. She glances at me and immediately turns around and starts walking in the opposite direction towards the professor as if to ask him a question. I then interpret this as her attempt to dodge me so I immediately walk out without saying anything to anybody. Right now, honestly, I'm feeling deflated. But I'm wondering whether anyone has some advice on what a next move could be so as to ascertain whether its already over with this girl.