First off you need to put the heat mat outside the cage. The snake can't tell if it is too hot and will get burned. You also need a thermostat. Heres a good one.
http://www.reptilebasics.com/Ranco-E...d-p-16172.html
you should also get a digital thermometer such as an accurite. You can find one at wal mart for 12-14$. we really need to know the temps and humidity before we can give much more suggestions.