Nothing, just accept that you made a mistake, forget it and move on and don't make that mistake again. In Satanism we don't obsess over our past mistakes nor do we beg for forgiveness like xians do, but we learn from them, resolve not to repeat them again and forget them.
There's nothing you can do about that one event, at this point. Dwelling on it won't change anything either. If you are already aware of the implications of this, just ensure that you do not repeat the same mistake again and move on.
Calm down please, it was just sex. The true problem starts if you do that for a long time or have a mixed race child.
Usually when one have sex there is an exchange of energies and a bond is being built therefore the persons getting a bit confused... of course this could be solved with soul cleaning but given the fact that we live in a world where people race mix like dogs and have the spiritual power equal to that of a rock yeah.... their souls are very dirty so stay away from them please.
You could start doing the Race Awakening Ritual daily to minimize the psychological/spiritual affects race-mixing caused you: https://satanslibrary.org/Rtrs/RTR_English.html
It is at the bottom, Other Rituals. Depending on your race, do the white Aryan one or the Black one.
You could also change/tweak the affirmation to suit your personal needs better.