GRABibus is right 90° is way too hot. I believe your heat mat is too large. you should only need a 4 to 8 watt UTH placed on the side of the tank. The bulb you're using isn't good. You shouldn't use Fluorescents or any kind of UVB bulbs. Switch to a UTH for a 5 gallon tank or a 10 gallon tank. Buy a Fluker's 5.5" Clamp Lamp with dimmer switch so you can adjust the amount of heat and light produced by the bulb. You should only use incandescent bulbs no higher than 50 watts. Look into Exo-Terra bulbs. A basking spotlight with concentrated beam for day and a Heat Glo Infrared for night.

Day temps should never exceed 85° and not go below 80° Until night. Night temps should range from 75° to 79°, but you'll want to hover around 78°.

Humidity should be 80%.

The position of you're temp and humidity gauges should be positioned in the dead center of the back wall 1.5" to 2" above the substrate. This will provide a more accurate ambient air and humidity reading.

Try these changes immediately and keep us posted.