If I were you.....
glad I'm not
Tell her even if she keeps it you will not marry her and that it would be a mistake for her to have this baby.
She might consider adoption but may change her mind after birth, then you get to pay child support for 18yrs, unless she let's you give up rights to it but she will most likely take your money because she can.
Also, bitches lie about this crap all of the time, did you stop calling her or end it recently? They like to throw that up and see if they can pull you back in, then in another few wks she'll have an magical immaginary "miscarriage" and things will be back to normal.
I would test her ass so you know if she is BS'ing you, if she is move on, if not you will not be able to force her to get an abortion if she does not want one, then it gets ugly.
Good luck