help me please

Rose
on thrusday I had un protected sex with my boyfriend. I wouldnt really call it that. but he went inside of my a few times then stopped because he realized I was scared.. Im 16 and hes 18. I know Im young and stupid for having sex but I dont know if he had some pre cum or not. I looked it up and theres a slight possibility to get pregnant for pre cum. I was in my ovulation session I didnt even know. and had 9% of pregnancy. Im so scared right now because yesterday and today Ive been having cramps. I havent told anyone that Ive had sex because Id be kicked out the house but I was thinking of telling my sister (26) but what if she makes me by see him anymore.