Make a joke of it. Don't be embarrassed - we all do things like this sometimes.
Email the person and say that you goofed, your mind was disengaged, whatever, and that you thought the meet was at your pool. Ask if they need you to do a basket, or if that has been covered in the usual way by the other team.
It may be that the person who received the email didn't read it carefully, and just thought that you were kindly volunteering to do the next basket for a home meet.
If the other team has actually been contacted, then you should do it, but just laugh it off.