For a small wound, Maracyn is not that necessary unless the fish suffered bacterial infection. Stick with daily water changes. You did not have to add Melafix.
How can you be sure it isn't anything else? Judging from that patch, I'd consider isolating it in a 5g hospital tank and monitor for possible bacterial infections. Keep antibiotics away from your snails. Melafix can't hurt. Dose with Pimafix as well as a precaution.