Question about tank placement, and heat..

Well I just picked up my ball python the other day and got the tank setup. Hes feeding great ( I work at the store I bought him, so I fed him ) and we feed all snakes before they even go for sale.

Anyways, I assembled my tank yesterday and was changing the water this afternoon and felt the aspen/bed a beast bedding and it didn't feel warm what so ever. I checked the Heat Wave ExoTerra pad and it was warm, but not as warm as I would think for 90 degrees.

Its a 20 gallon glass long, and its around the corner to a air conditioner unit - not in direct air flow either. My fish tank was there and it always read 80 degrees and I never had a heater in it. I am planning on picking up an accurite digital thermometer but the only one they had at walmart was an opened/stapled package so I was alittle hesitant to buy it and was hoping they'd get more in.

I am wondering if I need to get some sort of lamp as well for the cool side.

Anyone provide any input? I guess I really don't know or can't do much until I get a thermo reading..? Anyone give me some peace of mind!?