This time, with focused attention to accurate 1/4" seams and using the "no-waste flying geese" method (which meant less bias edge contention and increased accuracy), the finished block measures 18.5". And I like this turquoise fabric even better. So it is a win!
Meanwhile, I am nearly done with a sequin tank top made from the failed dress parts. A little bit of hand stitching and some hems to go. I'm feeling the garment bug right now, so I think I'll focus on clothing for a bit. I've traced a few patterns and look forward to getting some cutting done soon!