I remember having issues in the rear corners also. I had one side that was too sharp in tha angle but was able to force it back in shape when I dropped the floor in. Another thing you can try is applying a little heat to your seam to relax the resin a little. Heat will make it temporarily pliable again. I hope this helps. Dont get discouraged. It will all come together eventually. The cool thing about this process is that it is very forgiving. Yes, you can always get the saw out and do over.
Cheers