Jimmy - you said you two were studying and she just got up and said goodby. Go back to that conversation and try to figure out what you might have said that resulted in her not wanting to communicate with you any more.
I find that some fellas let out some kind of obnoxious remark that is a TOTAL turn-off to certain girls - and that's it. I can remember a few situations myself when a guy did or said ONE something and that was IT for him. (Granted, I was very young, but that's what young girls do)
Call her and tell her you are afraid you may have said or done something that offended her and would she like to get together to discuss it.
Do NOT text this very important message to her.
(Be prepared for a brutal confrontation in a conversation that could put blame on a range from bad breath to a comment you made. )