Human heating pads can not be used safely. It is also vital that your Ball Python has a basking area for proper digestion and overall health.

I'd suggest picking up a reptile heating mat ($15 or so), and a dimmer from the hardware store ($10 and under). The dimmer will allow you to control the intensity of the heat. You can also pick up a sheet of flexwatt and wire your own heat pad. Flewatt would be the cheaper method, if you can find some locally.

Please post a picture of your enclosure.