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It is possible to get pregnant in this situation, but the primary reason would be due to pre-ejaculate fluid, rather than any ejaculate fluid that remained in the urethra after ejaculating in the restroom.
The pre-ejaculate fluid has much less sperm than ejaculate fluid, so the likelihood of pregnancy is far less, but it is possible to get pregnant from a sexual encounter in which no ejaculation occurs.
Since she had her period, there is no reason for you to be concerned. A heavier period on Thursday would not be due to a sexual encounter five days before, but the fact that she had a period would typically indicate that she did not get pregnant from the sexual encounter.
For future reference, though, it would be better to use a reliable method for birth control, rather than relying on withdrawal to avoid pregnancy.
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