Pregnancy possibility??

About 2-3 weeks ago, I had unprotected sex however boyfriend did pull out, anyway I realized that night that I was on my last pill of birth control. So I took the last one and then realized that I wasn't able to get more until next week until our new insurance cards came. So what's the possibility that if I did get sperm inside me that it would last long enough while I was off birth control for a few days to get me pregnant?