The chances are slim, but pregnancy is possible. If this was less than 72 hours ago, I really urge you to go to your local pharmacy and purchase the plan B pill. This will prevent pregnancy and ease your fears and worries.
If it was longer than that, still try to relax. The chance of you being pregnant is tiny. The sperm likely died. So try to keep your stress levels low so there's nothing to throw off your period. Hopefully it will come just as it usually comes.
As long as you're not pregnant, I really urge you to talk to your doctor about birth control. Using condoms is great and really safe and responsible of you. But you've learned the hard way that mistakes can happen. Being on birth control gives you that extra coverage so you don't have to worry when something like this happens.
The best of luck to you.