long story but i need serious help!!

So I am 16 years old and i have been with my SO for 1 year 2 months, 3 weeks ago or 4 we had unprotected sex and he pulled out. When he pulled out there was sperm on his penis and it was watery so it wasnt full of sperm or so, ghe sperm didnt go inside me but we qerent 100% sure. That day I was on my period and it was the day before my last day. When I woke up I had brown period on my underwear because it lasted. Tomorrow is my period and we are scared to death if I am not pregnant or not. I have been crying the whole dy thinking if it won't come or not. I am a little sure that I amnot pregnant but I am very very scared?