Looks okay, the shiny side is it facing into the cage on 2 sides ?? Also if you find its making it too warm just poke holes in around the tin foil or take a bit off, one the sides.
Or if theres not enough light getting into the cage anymore just take off the tin foil on one side that will give it that light.
You could probably get away with not having the che on all the time too, otherwise it will be dangerous, you'll need someone who can always check on the temp as you dont have the thermostat yet.