Trust the Pill?

A few days ago my boyfriend and I ended up having unprotected sex and he did finish inside of me. It was the last day of my period when it didn't really affect me besides that morning before it happened. At the time I had taken 27 pills, so the last one of the pack was that night. I started taking them the Sunday after my period ended and started taking th pills in early August. My prescription says the pills are effective after 7 days, however I've read that if you start it a little later, wait a month. I'm just wondering if 27 days was enough to trust that I'm protected?