Does your digital thermometer have a probe and if so, where is it positioned? It should be right on the cage floor, usually in the warm hide, with the digital unit itself on the cool side. Also what are the temperatures of the room the snake's cage is in? And how far up off of the heat mat is the cage? It doesn't have to be too far up...just enough to let a bit of air flow in between the mat and the tub. I have my tubs only about a centimeter or two off of the heat tape myself.