How to save a friendship?

The title is a very broad question so i’ll give more context: Basically, at the start February or so, me and this girl (I’m a guy) became friends. Or somewhat friends, at least. We had a couple mutual friends, so we would always talk about them.

Recently though, she’s been hanging out with our mutual friends more than she used to, and less time with me. I really liked her too, and I thought we had a good thing going. I don’t want to lose her, as the school year is almost over and I don’t have her number. We’ve been growing distant for no apparent reason. There hasn’t been a huge argument or disagreement. I don’t think i’ve done anything wrong, so i’m quite confused.

Anybody have any ideas for me?