Ouch, yes that appears to be a burn. Snakes suffer in silence & it's hard to know how serious this may be...Silvadene cream for healing, and sometimes antibiotics
are generally prescribed by vets to deal with secondary infections (some skin may be sloughing off). I'd recommend a vet visit! If he hadn't shed recently, a slightly
pink underside can sometimes mean a shed is coming soon, but sadly yours looks like a burn...too bad you didn't set up his home with a thermostat in the first place-
BPs need such high temps (about 90* max) that it's very easy for uncontrolled heating devices to exceed that & cause harm. I'd continue with the paper towels for
now, turn down the heat and REGULATE it- you might be able to use a rheostat (lamp dimmer- available in all hardware stores) until your t-stat arrives...it's important
that he not get further injury. And now you know why we say you need to measure the temperature under the substrate, where the snake can contact the hottest
part...because sooner or later, your snake will push his way under there. The deeper the substrate, the more in insulates the UTH & can cause over-heating, which
besides burning your snake, can also cause a short in wiring & a house FIRE...so for your safety, FIX this NOW. His pink belly "worries you" but it HURTS HIM.And it could even burn your house or apt. down.
You'll want to find a vet that specializes in exotics & has snake experience:
https://arav.site-ym.com/search/custom.asp?id=3661