Heating Up Tank/HELP

Hello!
I bought my first Ball Python yesterday and it is in a 40 gallon long aquarium.
I don't know if the temperature gauge is broken or the cage is really cold (75 degrees HOT SIDE)
I need help warming up the tank, do any of you have suggestions?
Currently I'm using a 100watt Heat lamp

Do you have an under tank heater? A ball python really needs one hooked up to a thermostat to give them a good hot spot. Covering 2/3 of the tank lid with tin foil helps keep in heat and humidity too.

No I don't have an under take heater :(
I'll go buy one now!
And some people say covering half the tank with a towel helps, is that true?

Covering the tank with anything helps, but the tin foil will more effectively reflect the heat back into the tank. You could do both if you wanted to.

Either way make sure that UTH has a thermostat, they will get too hot without one and you could burn your snake. I use a Hydrofarm brand one specifically for heating mats.

We need more information before you run out and buy a uth as they do not heat the air. Personally I would hold off on the uth until you can order a good tstat. The ones at the pet stores are usually junk. I like Herpstat made by SpyderRobotics. http://spyderrobotics.com/home/products.html Many also use these http://www.reptilebasics.com/thermostats When it comes to a tstat buy the best you can afford. If you buy cheap you get cheap. The tstat is the most important thing you could buy for your snake. I had a Hydrofarm once and it broke within three months in the on position. Be careful with what you buy and do your research. Search the forum and find the pics of the snakes burned buy faulty devices and even melted tubs.

I uth is not a must but they are nice to have. However, without putting it on a good tstat it can cause more harm than good.

What is the room temp? Does I fluctuate through the day or night?

I have a 40 gallon tank in a room that stays 68. To keep the temps in a good range I use a 100 watt che on the warm side paired with a uth on a tstat. On the cool side I have a 60 watt heat bulb to keep the temps up. I have the screen covered in foil wrapped cardboard and three of the sides covered with thick art paper. I tell you this to show you that it may take a lot to properly heat the tank depending on the temps of the room.

On top of what KMG and everyone else has suggested, you should really just check out this tutorial on how to set up a tank. Follow this as closely as possible, perhaps implementing some of the suggestions by KMG, and you'll have a MUCH better set-up for your new snake!