You need a thermostat or rheostat for that heat pad!
A thermostat is a device where you can set the temps and it will maintain a relatively constant temp for you (within a range).
A rheostat or dimmer is a device that will control the heat output on the UTH but needs to be adjusted. It has a dial on it and you need to be checking the temps every day or so and if its too hot or too cold then tweak them a bit.
Thermostats are less work ultimately - but more money.
Dimmers take more attention paid to them, but are cheaper. YOu can buy them at home depot for 10$ (in the lamp dimmer section - get the plug in variety)
Also, if this is a baby leo (you mentioned you just bought it) then it should not be housed on sand. Washed, fine grain playsand can be an adequate substrate for adults but it should not be used on babies who are more prone to impaction. Paper towels, non-adhesive shelf liner, reptile "carpet" or tile are all suitable substrates for babies.
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1.1 Bearded Dragons
2.2 Leopard Geckos
1.0 Uromastyx (Mali)
1.1 Corn snakes
0.1 Mexican Black Kingsnake
1.0 Bairds Ratsnake
1.0 Rosy Boa
1.1 Green Anoles
1.1 House Geckos
0.0.2 Flying Geckos
0.0.1 Red Eye Tree Frog