It really looks like a burn. You say you have a T-stat? did you have the probe on the glass between the uth and tank? I guess I am questioning because a vet trip is now in order but assuming it is a burn you need to get the heat under control before anything else clean and dust free is very important but making sure your snake cannot still become burned (if the guesses are correct) further is also super important!

Do you know what the ambient air temp was when the burn happened?