ii feel like i should not say it is impossible, but it is impossible. 1- you can only get pregnant when you are ovulating, which is not right after your period. 2- there needs to be intercourse to get pregnant. 3- it takes a lot of sperm to travel for one of them to reach the egg. but, good to be concerned and responsible. if it were me, i would not worry about it. nevertheless, i recommend getting on some kind of BC, so you don't have to worry in the future.
The few little sperm introduced would have to be superheroes to reach the bullseye. It's theoretically a possibility as is winning the lottery. Very, very, very unlikely.