I would suggest that you get a rheostat, or a thermostat, asap (to regulate the heat mat's output/temp). If your snake burrows, it could wind up being burned on the glass (which could = vet bills, &/or a "compromised" snake, &/or... depending... worse). In the meantime, you may want to turn off the heat mat.
Although it should be okay (snakes can be just fine, at house temps, as long as not fed if temps are low)... If you worry that your snake would get too cold (if your house temps are very cool), before you get a rheostat or thermostat,... use an alternate heat source.
The glass should be of a comfortable warmth/temp and should not be burning hot. Check the temp, of the glass, after you install a rheostat (allowing time, for it to adjust, first) &/or, if using a thermostat, set it to an appropriate temp.
The mat does not need to be very hot for its heat output to rise & warm the substrate.
Also, I do not know where you are measuring your temps from but ... temps should be from substrate level (IOW not the ambient temps from partway up the glass/tank, etc.).