As this is screwing with you pretty badly I'm going to cut the shit and just be as plain as I can here.
Well, you certainly didn't make the smartest decisions, but of course that doesn't mean this girl has the right to pin a charge on you for something you didn't do. First of all, what's the exact definition of rape? Lesbian rape happens, even though women don't have an appendage to force into their victim. Gay rape happens, even though a man's anus isn't the same orifice as a woman's vagina. So what, or where, is the exact difference between molestation and rape? It's a gray zone to be quite frank.
Of course, this is pitched sideways even moreso by the fact that you stopped when she told you to. Although neither of you gave any verbal indication before you penetrated her, you responded immediately after she told you to. Although the communication between you two wasn't crystal clear, you still obeyed the consent clause.
Although at its core you didn't do anything wrong, there are several things you could have done to prevent this. For one, fucking on a first date isn't always the smartest idea. I'm not going to lecture you on how sex is sacred or any bullshit like that because it's your choice, but consider what's going on right now. For your own protection, it's best to know you can trust someone before having sex with them.
Second, and more importantly, there are more tactful ways to express the fact that your motives were purely sexual. When you told this girl you didn't want anything to do with her after she said no, well, that was just a stupid move. You could have at least given it a bit of padding, like apologizing if the two of you were looking for different things. Obviously there's a discrepancy in interest here. I think that has to be brought to the surface.
I don't know this person, and it sounds like you don't either, but if I were you I'd contact her and try to talk it over, fast. I have absolutely no idea how developed either of your abilities to rationalize or communicate are, but it's the most civil way to get this taken care of.