I need help

Guys first of all please don’t judge me I know that I was irresponsible.

So the thing is I had unprotected sex with my boyfriend underwater, today . He pulled out, and my period is due in 4 days. Should I take a plan B just in case? I read somewhere that plan B only stops ovulating and does nothing if youre past ovulating. I’m confused. If anyone have any recommandations It would be highly appreciated💞