Wait. Don't react. Nothing else you can do.
If she *is* pregnant, meet her to discuss your options. Preferably with a mediator of some kind, like your parents or a trusted friend or doctor (actually, nurses are probably better at this kind of thing). Let her know clearly, but *calmly*, whatever you are/are not prepared to do. E.g. if you will not marry her, tell her so up front that she will be a single mom if she decides to keep the child.
She can insist on financial support from you, sorry, that's the price for not being more careful. But she can't force you to be a part of your child's life or hers.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh