How do I control the temperature of burnt sugar?
There's a bit of misinformation in the answers and comments here I'd like to clear up. 

Tobiasopdenbrouw's suggestion in his comment that a thinner pan may work better is a good one. A thin aluminum pan is an excellent conductor of heat which is precisely why it would help in a situation like this. It is far more responsive to taking the pan on and off the heat. A heavy pan has a higher thermal mass and is thus slower to respond to changes in temperature, and it will have more carryover heat. 

A thinner pan will require more attention from you as it gets near your target temperature, but it's a lot easier to put the brakes on. As you approach your desired temperature take the pan off the heat frequently to check it's temp As soon as you take it off it will quickly stop heating -- there is only minimal carryover heat from the pan, and no magic carryover heat from an other source.

Additionally, adding more sugar will lower the temperature. There is no "solution" that can crystallize. A solution requires a solute and a solvent. There is only one substance present in molten sugar -- sugar.

Spraying water on it is a terrible idea and I advise against it. At best it simply vaporizes instantly to steam. At worst it spatters molten sugar on you, not fun.

In short, treat it like you would a pot of water that you were trying to maintain at a specific temperature. If the water gets too hot, you'd add more water or take it off the heat. The same applies concept to molten sugar.