Oopsie

I recently made this really awkward situation where I accidentally sent a private joke to the wrong person in our group chat. It was meant for my best friend, but it ended up going out to everyone. The message was about us mocking one of our mutual acquaintances, and now I'm pretty sure that acquaintance saw it. I feel so embarrassed and guilty, I never intended for them to know we were talking behind their back like that. I've been trying to think of a way to apologize or explain, but I don't want to draw more attention to what happened. It's one of those things where you wish the floor would just open up and swallow you whole.