KR

I haven't made this pattern but have made LeMoyne stars which uses the same construction of the 8 vanes. But first, instead of cutting all those diamonds, you could strip piece and cut slices on the angle needed, then sew the slices together for each vane.....perhaps trimming after to achieve the correct size & angle.

Sew 2 vanes together four times. Press seams all in the same direction. Sew 2 sets of two together and press seams in the same direction.

Then, as you've found, the true test is the last seam....make sure your centers line up. I found it easier to start stitching in the middle and go out to the edge....or baste the middle by hand to hold it in place when you're sewing with the machine. Go slow over that middle seam.....there's a lot of fabric!!

Gotta run! Good luck!