If it's a wooden enclosure, you'll need to get a RHP (radient heat panel) to provide the ambient heat or find another way to provide it. The UTH is there to only provide belly heat which doesn't do anything to heat the ambient air in the enclosure.

Also, your thermostat probe should be placed between the UTH and the bottom of the enclosure instead of inside the terrarium. What thermostat are you using? Your thermometer probe is placed correctly in the tank on the hot spot of the UTH.

Post a photo of your enclosure. You can do it through your phone if you download the Tapatalk app.

I'd suggest waiting on purchasing the bp and make sure that your temperatures are correct.