Hey

Make sure there is adequate ventilation, usually a full screen top is only half covered. I have a full screen top. I can't believe that the heat mat is only reaching that temperature. A lot of brands can reach a temperature of 100F directly on the heated glass, a thermostat is always essential to control their output (you can't adjust the heat by wattage as you would with bulbs) Use a digital thermometer and place the probe under the mat for a proper temp reading, it will be warmer than the top and your frog will be spending most of its time burrowed. Temps should be above 80F during the day. Having said that, most keepers use spotlights since they like to bask and it's more natural. No need to pay attention to humidity, just keep the substrate moist