Okay.. Here's the thing.. Sperm.. When they get inside you, they go in the vagina, which is a very acidic place and about half of them die.. Then they travel along, until they get to the fallopian tubes(there are two). The egg is only in one of these tubes, so another half of them are lost when they travel up the wrong tube.. Annd also, theres only an egg for about 48 hours every month(ovulation).. In most women, ovulation occurs about halfway thru their cycle(about 2 weeks before your period is due)... So if you got your period the next day, u probably werent ovulating anyways
simply put, its a slim chance..
If your still worried, wait a couple weeks and take a home pregnancy test.