Cycle flow

Destiny
So I need some help , I had sex on the 7th forgetting my period was suppose to come the next day. But now it's been 3 days and still nothing. Does sex really throw periods off? Because like a week or 2 ago I had sex and there might have been a slight chance he came in me. I'm scared I'm only 18 and it's killing us both right now 😔😔