My first mistake occurred while building the frame.
I read the manual first, honestly, but by the time I glued and screwed the butt blocks to mold frame 3, I had forgotten the warning on p. 24, so I had to cut away part of two butt blocks.
The mishap provided my first experience with a Japanese handsaw. The cut on the other butt block is cleaner. On the second attempt, I seemed to be sawing into the mold frame, so I started over. the cut in the butt block is beveled, and I restored a smooth surface to the mold with the sander.