that temp gun is perfectly fine and will do great. They perform just as good as the $50 units for fraction of cost.
I use them as their cheap to replace and work great.
But you def want to know the surface temp of the glass of the hot side. If your using a dimmer my guess is that glass is pushing 105F when covered with cyprus. If this is teh case, thin it out or go to papertowels. Always need to know the hottest point the snake can get to. If its 90 on top of bedding then you know its hotter below.
get the temp gun asap to confirm your surface temps on the bedding and on glass.