Brazilian Rainbow Boa Help

Hello
i just got my baby male brb yesterday and he is doing great. However, almost everything i read said they need temps at 80-83 degrees, and i cannot get the temp up. I have one heatpad on the tub currently that is connected to a thermostat. The temp has been staying at 78 degrees, is that okay for him, or does it need to be higher? I tried plugging in another small heatpad but it makes my temps go crazy high. My humidity is perfect, it has been staying in the 90s.
Here is some info about the setup:
66 qt tub
air holes all along the side and lid
cypress bedding
large waterdish
decor
heatpad
thermostat
wet beach towel on bin lid

That's not bad for an ambient. What's your hotspot?

Move some of the cypress away from the under-tank heater and measure the surface temperature of the tub floor over top of it. If the tub floor is in the mid-80's with an ambient in the upper 70's, it's fine.