I pulled out the hat I’d almost finished on the airplane home.
In the dim light there, trying to get as close to finishing as possible while the number of stitches left on only one circ (the other one had ended up in the overhead bin this time) kept getting smaller and tighter, it turns out I had goofed.
There was nothing for it. You never regret frogging when you know you need to. I did, finished the new top of the thing, got it right, and bam! It is done.