What would you do if you were me?

I was late to my cl so i parked my car and i was on rush climbing stairs to my cl, i bumped into a girl and she ended up dropping her books and purse. After helping her get up and getting her stuff together (and apologized her million times) and talked with her tried to explain why i was running and stuff. Couple weeks later i went to computer lab to print something, some girl touched my shoulder and said "hey" (at first i didn't know it was her and stuff...) she wrote down her number on a peice of paper (i think she did that before she came up to me) and gave it to me. So i gave her my number to her too. She asked for a lunch as a repayment (i guess for bumping her?). I have a girlfriend and very much in love with her. Should i call her? and if i do what should i say? I don't really want to go because my gf is jealous (like extremely) and she might not understand it.