I would take a short trip to WalMart and get a human heating pad. It can stay on 24/7. Place it under one side of the enclosure, 1/3-1/2, and turn it on low. Also, while at WalMart, get an Accurite Digital Thermometer/Hygrometer, it's $15, and will save you so much trouble. The little stick on thermometers and humidity gauges are very inaccurate and when measuring with those, you could be freezing or cooking your snake.

Since most snakes are nocturnal, UV is not needed. Just provide a 12/12 day/night cycle and your snake will thank you.

Burrowing into the substrate could signal being cold, but it could also show the snake isn't feeling secure. How many hides in the cage do you have? One or more on each side, one on warm end, one on cool end, will solve that problem. Make sure the hides you pick are nice and secure, clay pot bottoms, you know the ones that sit underneath the clay pots, are awesome, you just knock a hole into one side, and the snake is happy.

Garrett, Wally World will end up being your best friend. They don't realize that they actually have a reptile store on their hands...

With that light, you "might" be able to use it, but I would rather save yourself some money, and take it back. Depending on how much the heat pad heats the enclosure up, you might not even need a light. The light from a window or other light source will work great.

The boa caresheet here should be able to tell you pretty much everything, but if something isn't clear, just ask. It's a friendly place around here Good luck with your new boa