Calcium sand is nasty stuff for snakes to live in.. sand boas do not live in sand. I use aspen for mine.. and they do need humidity! 50-60% is very good for them.
You said you have a 'tank'.. how big is it? A baby sand boa is going to be quite shy and a small cage (like a shoebox) is going to be much better for it than a tank.
Do not let the temperatures go below 80 degrees.. no night drops. If you must use a heat lamp instead of an under tank heater + thermostat, get one of the red bulbs or a ceramic heat emitter instead of a white light bulb so it's not bright at night.
