Personally, I'd say it's not yours... or perhaps she's not even pregnant. This sounds fishy. I know that unless the baby is genetically deformed or something they won't do an in-utero DNA test (because they'd have to do an amniocentesis which is dangerous and painful), so you will have to wait until the baby is born. Do NOT assume this kid is yours, and do NOT let this pregnancy affect your life in a negative way (ie, don't let this girl play the emotions game with your head)
I'm very very happy there are men like you in the world who take responsibility!
__________________
Sage knows our mythic history, King Arthur's and Sir Caradoc's
She answers hard acrostics, has a pretty taste for paradox
She quotes in elegiacs all the crimes of Heliogabalus
In conics she can floor peculiarities parabolous
-C'hi