Me and t.his girl arn't officially dating, but I told people she was my girlfriend, and she found out!?

Well the cat is out of the bag but the damage is controllable. You said girl-friend and that can go either way. yeah most people mean a relationship but you would also call someone that you were casually dating a girlfriend too depending on your age. I would suggest to not mention it again dn see how your relationship progress. If you are looking to get serious with her then you will need to know at some point where the 2 of you stand. You would hate to find out 1 day that she is seeing other guys because the 2 of you are not in a relationship. .Hopefully she will come around. Happy Holidays.