The only thing you can do now is just wait to see if she gets her period next month. It is a myth that you cannot get pregnant on your period. And even though you only put the pre-stuff into her, just remember, it only takes one of those little guys to get a girl pregnant! But, try not to worry and just wait. If she is not concerned, do not worry her, because if she gets stressed out about it, it can cause her period to be late. That would just make you both more stressed. Good luck, and next time use a condom.