How long sperm remains "present"
If you haven't washed for three days, then there's likely to be semen left over. You shouldn't worry though, as individual sperm cannot survive the outside environment for more than a few hours. If you were to have sex again without washing (and not using a contraceptive), then she should not get pregnant. Don't take this at face value though - make sure you use protection!
Inside a woman's body, sperm can live for up to seven days (most commonly three to five) waiting for the egg. They will swim through the uterus to the fallopian tubes where they will fertilise the egg. To prevent fertilisation, the woman can take different types of medication provided by a doctor, or at a pharmacy.
Semen's role in getting pregnant
Semen is the fluid in which sperm live, and semen on its own cannot get a female pregnant. You can only get someone pregnant if the sperm is present. To make sure that pregnancy does not occur, remember to use contraceptives.
HOW LONG DO SPERM LIVE?
SAFE AND HEALTHY SEX