My previous cat had a scratch like that and I kept doctoring it, however, couldn't see that it was infected until it starting seeping. She had to have surgery to clean out the wound and cut away the infected area, and essentially had a "butt tuck". I think it was over $200 all said and done. I would get your baby into another vet to look at it and get some antiboitics started. Better not to have to put your cat through a surgery and certainly less costly! Vet thought she might have got in a fight with another cat, didn't really look that bad to start with.