Scared

I'm over a week late on my period and it's stressing me out which I know can make it even later. I had sex like 3-4 weeks ago and we used a condom but in the middle he decided to take it off and not tell me, I realized like 15 seconds after and told him to put one on. I'm just scared that that 15 seconds could've gotten me pregnant. Other details: 19, not on birth control.