Hi,
Three hours isn't that long - we normally advise people to have the setup assembled an running for 12-24 hours before trying to put the snake in it so they can adjust things.
It is common to have to set your thermostat higher than the desired temp to get things dialed in but this depends on where you put the thermostat probe.
What kind of thermostat is it?
Be very, very carefull trying to run a UTH without any form of control - some brands can get to 120f+ and that is more than enough to burn your snake.
I usually have the hot end of the tank as one third. Also a lot might depend on your ambient room temperatures - what are they at the moment?
I would put the probe of the thermometer under the substrate and hot hide.
dr del