I need some advise guys!

So, I got my cage set up....
No snake yet, so I've got time!
I have a 20L With a small UTH.
I plugged it up, just for kicks and guess what? You can't put your hand on the bottom of the cage for more than 5 seconds. I pretty much knew that would be the case.

So, back to the store I go and this is what I came home with.



Is this ok for a temporary fix?

I have read the instructions and saw on the internet on how to set it up.
This is where the frustration comes in!

Do I put the probe inside on the bottom under the substrate or do I put it outside on the bottom between the glass and heat mat?
I am seeing it both ways and want to know opinions on which is best.