Plan B

I lost my virginity the other night whilst extremely drunk. I was aware of what was happing and my ex came over and it just happened. When we were having sex he said the condom fell of whether he was lying or not in not sure. He said he pulled out but I'm not on the pill so I took plan b the next day. I'm still so worried that I'm pregnant even though we had sex on the last day of my period. Is there anything to be worried about ?