condom ripped

Last night my boy and I did the deed and halfway through it, because my vagina wasn't lubricated enough it ripped but it was when he was slowly putting it in and the thing snap. And he took out immediately. (His dick wasn't all the way in) I'm worried that there's a chance I might get pregnant. The thing is, I was on my period when we did it, there wasn't any cum at all (might have Precum that's why I'm worried) and I'm on BCP Alysena 28. Should I take ECP just to be safe? Is there a slight chance? Once in awhile I am pretty inconsistent with my BCP. What are the chances ?