You need a gap between the bottom of the UTH and whatever the enclosure is resting on. It kinda seems like all your heat might be going into the towel.

Do you have a probe thermometer to check the surface temp? If the herpstat is reading the probe at 100 then I am inclined to believe the herpstat over the infrared. What kind of infrared is it?

It could also be a crappy UTH. They sell Flexwatt at the AAE and I'm sure they have some already wired up, or they will wire it for you. A heat lamp will do fine for the short term, but I think belly heat is beneficial since that is where the snake hangs out.