Plan b pill does it work?

Early today, my boyfriend and I had sex. We had a condom but it broke. However, he did pull out before cumming in me. We went to the pharmacy to pick up "The Morning After Pill." The pharmacist suggested Plan B. It said it was best taken within 72 hrs and the sooner the better. The pill was take within 9hrs of having sex. I was just wondering if anyone knows if this pill really works and what is the likeliness that I will be pregnant.