Would this be rape or what?

It's not your fault in the first place. If it was rape was really up to her. She is the one that decides if was forced into doing into what was done. But you don't have very good legal leverage because on top of the supposed rape in question you have under aged intercourse and Drinking. A little tip for picking a relationship (of course I'm keeping in mind you probably knew this person prior to the incident) do you really pick the one who comes out drinking in her undies... honestly?