One of the most important lessons I learned from making a polymer clay mistake is always use a good thermometer in your oven..I learned this the hard way when I made one of my early projects. I worked really hard for several days to make it just the way I wanted it and I was so proud of what I did.
I put it in the oven and turned on the oven to the desired temp according to the knob and left it to cure. I went outside and came back in 1/2 and hour later to check on my piece and guess what the piece was scorched. Oh man was I bummed so I went to the store and got a good thermometer and put it into the oven and guess what the oven was 45 degrees hotter then the set temperature. No wonder my piece was ruined.