How to get the heat up?

[Jus1More]

So I bought a T8 AP cage, set it all up and I have a 11x17 ultratherm heat mat on a thermostat under it.

but I have the thermostat set to 100 degrees but inside I can't get it over 83. On the hot side? I haven't had a chance to measure the cool side yet but I'm assuming it's somewhere in the 70s. How can I get the heat up? Do I need to buy another heat source? The mat is flush against the bottom right now and the probe is reaching up to 1"" as its set to but my inside thermometers aren't getting over 84 ever. They're just going back and fourth between 83-84

It's the type of heat mat you are using (Ultratherm). Those mats do not put out enough heat. When I first got into reptiles I did a search on what type of UTH to use. Came across Ultratherm and thought okay... but when I set it up it wasn't providing heat temps where I needed them. Thats exactly what happen it never seem to get over 85 degrees. Maybe it's just a thing with these heat mats but not my cup of tea!!