IM FREAKING OUT

so about ohhhh say 3-4 weeks ago i had sex with my boyfriend. we had to stop because the condom broke and i am NOT on birth control. . . . well its about time for my period and it hasnt showed up. Im a little worried because both me and my boyfriend are a little too young to even think about raising a kid. Am I overreacting or is there a possibility that I am pregnant. keep in mind he never finished so as far as i know there was only pre cum that could have entered my body. . . . .