I did it! I’ve sewn all those 414 squares together (or at least, into their colour blocks). It felt like it took FOREVER, as I worked on sewing almost solidly for three weeks! With very little respite. There’s nothing quite like a deadline to ensure I get things done!
So here it is, in all its (almost) sewn up glory (the white is not as stark as it looks in this photo, it’s more of a cream colour)