You guys need to all relax. The snake is not going to die if it's left at room temperature for a day. I think about 99% of us are guilty of similar mistakes when we first got our snakes, I know I messed up big time!
That being said, do not feed the snake until you have your temps figured out. Ball pythons are pretty hardy, but they do require a proper amount of heat for digestion or the prey will just rot in their stomach. That's no good.
Move your thermometer down to where the snake is actually at. What is the point of measuring the temps at the top of the cage? The snake will never be there. You need to know what the snake is experiencing. Get yourself some DIGITAL thermometers. The accurite weather station is a popular one around here. I have 5 or 6 of these to measure my temps in various cages. You can purchase them from home depot, lowes, or walmart. It's just the basic weather station with a wired probe to measure the outside temp, and measure temp and humidity at the unit. So it's really the only thermometer and hygrometer you will need.
As for heat, a heat mat is your best bet, but if you can't keep your ambient (cool side) temps above 75º then I would suggest a low wattage red heat bulb on a dimmer to add a little extra warmth. A heat mat must be used with a thermostat to control the temp. If you don't use one, you risk burning your animal. It is a bit of an investment as the cheapest models are about $25 and go all the way up to $250. I highly recommend making an investment on a nicer thermostat now. I like the vivarium electronics that they sell at reptilebasics.com I have the ve-100 and the ve-300 dual zone with night drop.
Everyone eventually learns that pet store employees literally know nothing about the care of the animals they sell. Don't listen to them, they will just help you waste your money on useless and expensive equipment.