Pregnant

My period started the 8th and ended around the 13th. there are usually 29 days in between each period. I had sex three days after my period ended, and got some cum around my vagina, but I'm not sure if it went it. I wiped it off the immediately and washed the area. normal ovulation occurs 10-16 days before the next period, is there a high chance I could become pregnant? would taking plan b be worth it if I don't know exactly when I'm ovulating?