Thank you all for the advice, I have set up the terrarium as you told me to. But there is one thing that I'm not certain on. You said to set the thermostat for the heat mat so the enclosure floor is 90°. Did you mean the bottom of the terrarium or on the substrate? Because I set it for the bottom of the tank and it doesn't seem to be getting hot enough. And both sides of the terrarium are staying at the same temp. Should I just poke some holes on the cold side to let some heat out?
Bottom of terrarium is where you measure the temp. Snakes will dig down if they need to. The hottest thing your BP can touch should be 89-90f tops.
How big is the heat pad? Did you give it time to warm up? Not sure why both sides would be the same temp.