Is it possible that I've taken the pattern with the most pieces, decided to sew it with difficult fabric, and figured out the most complicated way to assemble it? I think, yes.
I laid one coutil side piece face up, and one satin piece face up. Then I laid the back ribbon panel on top, wrong side up, pinned together matching the notches, and sewed them together.
I attached the front ribbon panel the same way.
Then I took the other coutil side piece and pressed the sides in 3/8 inch. I laid it flat, face up, and placed the attached side panel, face down, on top of it. There should be the same amount of seam allowance straight across the top. I'm not sure how I managed to make the panels different lengths. Brother. I checked both fronts against each other, and both backs, and they matched so it's a patterning issue that will have to be fixed. But the only option at this point was to keep sewing, so I continued as if everything was OK and sewed across the top just between the sewn seams.
I graded the seam allowances, clipped the corners, flipped the coutil piece over, tucked the edges in along where I had ironed, and pinned the piece down with the folded edge just over the seam line.
The bottom edges were folded up and pressed.
Then I sewed on the right side of the fabric, from top to bottom, 1/16 inch from the seam line.
Finally, I sewed the channels for the boning.
Whew. I need a beer.