What? How on earth could this happen? Did you willingly and knowing violate their privacy? Draw near so as to hear the confession? No?
Open air, right? So, what’s the problem? If you are in the confession line, you know who is confessing, right?
Excommunication? Are you perhaps scrupulous? Please speak with father about this, as I think you are magnifying things that may not even exist.
Personally, I do not care if someone other than Father hears my confession. So what? God judges me, they don’t.