Me and my boyfriend had sexual intercourse i was on the last day of my period, we did use the withdrawal method but it was too late as he came outside my vagina, is there any chance i could be pregnant, i bleed for 4 days.

Small chance: On the 4th day of your period its less likely that you would get pregnant (but not impossible). The "withdrawal" method is fraught with peril. If you don't want to get pregnant, you should get on a more effective method. If you use this method long-term, you will eventually get pregnant. Best wishes!

Conception optimum: Women ovulate 14 days before their next menstrual period starts. In a 28 day cycle this would be day 14. Male sperm can survive for up to 5 days. If intercourse happens on day 4 of the cycle, conception is unlikely.