Sourdough

Hello Chef,
I have been working on sourdough.  My problem is that the while the top of my bread looks fine, the bottom is slightly burnt.  My internal temperature today was 208F.  I use an orange enameled dutch oven with white interior to bake, and I have a slightly different method of putting the boule in the oven since I am afraid to do it barehanded as you do.  I place it on a long piece of parchment paper and use that as a sling to lower the dough into the oven.  

I have been baking at 450F for 50 minutes.  Should I lower the temperature, shorten the time, or ...?