ok that's your problem. that thermostat isn't worth the plastic it was made out of.
The UTH you're using can and will get up to 130 degrees. Far more than enough to kill your BP. For now you need to get a lamp dimmer like this to manually control the UTH until your new thermostat arrives.
When you get a new thermostat don't even go to the pet store. None of the crap they sell there is worth your money. Here are 2 good thermostats:
1. the hydrofarm. Sold on Amazon for $30 these are the minimum that is considered safe. They aren't very accurate but will get the job done on a budget.