Yes, get rid of the sand. That could be stopping the heat a lot, (and just not a good choice).
I would get something better to measure heat, like a digital thermometer at least, with the little probe that you can put anywhere you want. I just got a temp gun, which is great.
You are definitely going to want to figure out insulating that tank somehow from your cold house. The heat pad could be too hot right now and the ambient temps could be too low still. Both those are dangerous. Do you have a dimmer on the heat pad? They can get burn your snake otherwise.
Also, using a heat lamp to compensate is going to dry out the enclosure. I noticed the glass is wet in the picture. Is that because you are having trouble with keeping up humidity? Heat lamps will do that.

So in short:
Lose the sand
Better temp reading
Cover up the top of the tank with a blanket maybe, (or like the top and back)? See if that changes things. (Obviously not with the lamp).

Anyone else have some good advice?