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It is very unlikely that a pregnancy would occur after ejaculation near the vaginal opening. Sperm travels from the vagina into the uterus through the cervical mucus. When deposited on the dry skin outside the vagina, the sperm will not be able to move and will die off where deposited.
Washing off immediately will also not only remove the sperm but the water will cause it to die.
Unless you have deposited the semen close enough to the vaginal opening to cause some to leak into the vagina, you have no cause for concern.
Even if a small amount leaked into the vagina, it would be too little and is unlikely to cause a pregnancy.