Hi Dick;
I would stop your build now and consider raising that whole core and cement board on clay bricks laid flat.
Sitting tight to the floor, that core will burn thru the cement board after? one season maybe two? After that, it's your flooring itself that chars.
If you raise your whole core build 2.5" or so, then your flooring is safe.
If left as is, you will have trouble down the line.
After the core the temps are low enough that you could sit cement board on your flooring if needed.