pregnancy scare

on june 19 i had protected sex for the first time w my boyfriend. he didn’t ejaculate in the condom because we had some fears. now (july 16) my period is 3 days late, but it almost always on time. around this time last year, i had a longer cycle also (41 days long) so i am hoping that this lateness is due to my increased exercise rather than pregnancy but i cant help thinking of it as a possibility. i understand the chances are probably low but i am 17 and any chance is scary. (although i understand i am responsible and i decided to have sex so i should deal with the consequences, i got prescribed birth control within the two weeks after having sex bc i knew i would feel more comfortable having sex on birth control).