can't get over the fact she had her period so soon!

I'm still paranoid but me and my girlfriend had unprotected sex this pass weekend. I know I didn't cum in her because I pulled out before it happened. Well a day later (monday) she had her period and lasted for 4 days. Although she was not suppose to have it until next week. She says her menstruation period was normal like the months before, but I can't get over the fact she had her menstruation period so soon!

But my question is there still a possible chance that she can get pregnant even after her period? Was this just a decoy for the worse things to come, or am I out in the clear? Please help me, I have been losing sleep over this for the past few days now.

Thanks!