Girlfriend getting jealous. PLEASE HELP?

i was working with this girl in basketball yesterday after school. i didnt tell my girlfriend because it never really crossed my mind when i talked to her. we just messing around after and it was just me and her in the gym, our school has a practice and normal gym. we were in the practice, my girlfriend had volleyball in the normal and she saw us thru the gl wall in the hallway fillin up her water bottle. me and the girl where just sitting on the bench and she was messin with my hair sayin it was lookin like that zac efron dude on hsm3 when he was playin cause it was sweaty and we laughed about it and my gf came in and said i see how it is and walked out i got up and went after her and i stopped her for a second and told her nothin happened i was just helping her and she pushed me back and went back into her practice. she wont talk to me. at all. it's been over 24 hours. wtf do i do?