If you're gonna do the deed, you should be prepared to face the consequences.
THat said, good luck, but remember that you have just as much responsibility as she does, and by saying that she was misleading about the birth control doesn't excuse your faultering of emotions now, after the fact.
Sorry to be harsh. In the end, I wish you the best, and maybe with time, this can resolve itself? COuld anxiety about the baby be the culprit, and a sense of not knowing how much is enough to love someone to make a lasting commitment?
Best of Luck!
~Lu