I'm not sure why you say that you "think" it's burning your clay. If you aren't sure, don't worry about it. In my experience, you'll always know for sure if your clay is burnt because it smells terrible and is browned. However, if you mean that the oven gets too hot when your oven thermometers show the correct temperature, then it's time to experiment!
Use some white clay or some scrap clay that's light in color (so you can easily see if it burns), and make several batches of simple shapes that are similar in size to your pieces. Bake a few pieces at the recommended time for Sculpey, but vary the temperature for each batch. Start at the oven's setting, then go in 10-degree increments up to what your thermometers show. You'll be able to tell what the right temperature is for your artwork and for your oven.
Good luck!