With lots of careful pinning, I managed to get the centre stitched together. Next step is removing the paper!
(I removed the paper from the seams that would be folded under so it wouldn't be permanently trapped.)
This is the result of 2 evenings of movie watching and paper removal! I took my time, and was careful so that none of the stitches pulled out. It was tedious getting all the tiny bits of paper at places where seams crossed over, but so worth it!