Welcome to the forums!
I agree with bcr, the only thing your UTH is doing is heating up that one spot, it's not helping with your ambient temperatures. I'd also like to know what kind of thermometers you're using because unless your room is 81 I doubt the inside of your tub is with just a UTH. You're probably going to need some type of overhead heat source.
jmcrook shared his quarantine tub set up and you can take a look at the link below. His was for a carpet python I'm sure, but the idea is the same and will probably solve some of your issues.
https://ball-pythons.net/forums/show...Quarantine-Tub
I know hindsight is 20/20 but in the future, I would recommend setting enclosures up and letting them run for a week, if not two, prior to bringing a snake home. That way you can make adjustments and fix any issues before your animal is living in the enclosure.