help!! broken condom!!

Hi, I'm 18 and my boyfriend is 19 and we're both freshman at the same college. We've been having a bomb sex life, but tonight he finished in me and we found that the condom broke. I've been on the pill for over a year and I take it everyday pretty close to the same time everyday. I'm super worried because this has never happened to me or him, but he offered to take me to the store tomorrow morning to get plan b. Is this right?? I don't want to have a baby, and I'm on the pill so I'm probably fine right?? Please help!!!