I have used athletes foot powder with good results, but not on an egg that bad. It's hard to say without seeing the other side but I don't think that egg has much of a shot. I would have probably put it in the incubator with the "good" side up but I don't know that it would have helped either. If it were mine I would probably still flip it but that's up to you. I bet the other 3 hatch fine. I would maybe put the worst egg in it's own box just because you are going to have to clean it every few days and it might be best to not have to disturb the other eggs so often. Good luck