Judging by the blisters, I'd say it's a thermal burn from laying on the unregulated UTH pad. At this point, You should use clean paper towel as substrate. You will need to get your snake to a vet as soon as possible for treatment to prevent infection. The best thing that you can do for now is to get to a pharmacy and get some Betadine solution and Neosporin (without painkiller). Dilute the Betadine in a tub of water and let the snake soak for a few minutes. Lightly dry off and apply the Neopsporin. There is also a burn cream that will help called Silver Sulfadiazine, but I don't know if it can be obtained over the counter, or if it must be prescribed by a vet.
And make sure you get the temps under control with a thermostat and a reliable thermometer to monitor the temps with. If you need suggestions for websites to get thermostats from, just ask and we can provide links for you.
Good luck to you and your snake for a speedy recovery.