I've been pestering my FI to get his friends addresses for several weeks, but he's in a very time consuming academy, (Law enforcement Ranger School for forest rangers.) So I got on his Facebook (with his permission) and sent a message to several people. Well, it was late and I was tired and I managed to send the message to Megan Y. instead of Michael Y. (They're siblings.) I wasn't planning to invite Megan, because we already have over 320 guests and FI is friends with her brother, and not her. (I also don't know Michael and didn't know he had a sister.) I didn't even notice I had sent it to the wrong sibling until she replied. Now I don't know what to do. We really can't afford to invite any more people at this point. Is there any polite way to tell her that I goofed and that I'm really sorry?