I like to deal with awkward situations with acknowledgement and honesty. Even more so if I made the situation uncomfortable for the other person and there's a big risk they'll continue to feel uncomfortable around me. So I would have a short conversation to clear the air, something like :
Now that we're working on a project together, I don't want things to be awkward between us. I'm sorry that I made you uncomfortable in the past, but I want you to know that I understand that nothing more is going to happen between us, I won't bother you about it anymore, and I just wish for us to be good co-workers.
That's it. Don't make this a big conversation, it will just make things more awkward. Don't also expect a response from her, don't make it her job to make you feel better about everything that happened. This is just to let her know that you know things have been awkward in the past, that you had your part in that and that it's not going to be an issue any more.
Then act like it. No more mentioning your crush, to you or to your colleagues. Act as if you have no feelings for her left (ideally for you, I hope you can really move on from her).
I've been somewhat in your colleague's shoes. Someone in a group of friends had a crush on me. I actually liked him, but had just gotten out of a serious relationship and wasn't really ready to dive in something serious. All our friends knew about this. They became more invested in the relationship then I was. In the end I decided not to date him. It wasn't my main group of friends, and I was quite new in the group, so I just faded out. It was just too awkward and uncomfortable, they couldn't let it go.
So if your colleagues continue to talk about this, ask them to stop. She doesn't have the option to leave like I did. Since you created this situation and made things uncomfortable for her, I hope you'll make some effort to make sure things get back to normal.