Incredibly awkward conversation today, I might be forced out of the closet soon!

I was talking to one of my friends today in class and somehow the conversation got on what had happened in chemistry a few hours earlier. In chemistry my project group was working on concepts for a chemistry related game and we ultimately decided to have a Wheel Of Fortune style game. I, jokingly, asked the only girl in the group if she wanted to be Vanna White. She said no, but one of the guys said they would be Vanna and were completely serious. Anyway, that was brought up in conversation and I jokingly reminded my friend that she had dated him at one point (She had dated him as a prank). She laughed and then told me that he was bisexual. I honestly was not surprised, but she followed it up by saying that he might have a crush on me. I know it is a joke, but she wouldn't stop saying it. She then said that she would tell my mother (Who she knows very well) that we're dating. My mother knows I am gay but doesn't know whether I'm dating or not. She continued on and on about telling people and I know she very well might. It's awkward because I'm not out to anybody at my school and she is inadvertently doing exactly what I fear. She isn't the kind of person to stop so this will probably go on. As for the guy she is talking about, I can see what she means. We probably could date each other if the world wasn't so stubborn.