Wait until next week. Offering immediately after a refusal is only going to stress the snake out more and cause more and more refusals. It is best to just wait until the next feeding day.
It isn't a big deal if the probe is sandwiched between the UTH and the glass or not. I have all my standalone tubs set up with the thermostat probe on the outside of the heat tape and it works perfectly. Just adjust the thermostat until the temp in the tub is where you want it.