Could I possibly be pregnant? Should I worry?

I have been using tri-sprintec 28 day regimen birth control for two weeks now. I had last night with my boyfriend, he came inside of me, we had no condom on. It was the 13th day of use. I have not missed a pill, and I have taken them at the exact same time each day. On the directions it says I need to use back up for the first seven days after beginning the pill. What are my chances of being pregnant? Should I worry?