I REALLY NEED SOME HELP WITH THIS!! PLEASE ANSWER.!?

Okay so there is this girl in my gym class that I really like. For the first two weeks we didnt really talk then I started to hang around her and her friend. So after looking her up on FB I found out that she likes the Boston Red Sox, and so do I. So I asked is she watches them and she said yes and that she wears her red sox bracelt all the time. So we huing out and made small talk for the next three weeks, and I added her on FB. And she added me within 5 min. I talked to her a few days later on there, and it was about a 40 min convo. So the next day she was on I told her I need to go but can I text you and she logged out really fast. The next day was awkward, but We are over that. It has been about 4 weeks since that, and we talk all the time in gym now. The end on the school year is next Wed. And I want to get her number. But I dont want to do it in person. How do Iget it without her saying no or logging out of FB??