Working on a 2-piece dash piece.
My template is the outline for the blind seam.. then I have to draw the seam allowance. I do it with a tiny template, inch by inch.
Here's with all the double-sided tape applied. I still use about 5-6 pins on each corner just to make sure the sew line is perfectly lined up since the tape won't hold.
The corners on the outer piece need to expand, so they must stretch to meet the inner piece.. this is why the tape is on the inner piece (since the inner piece does not stretch or bend while I sew the blind seam).
I'll then line all the edges up.. sew the blind seam.. then work on getting all the edges flattened so I can top seam them.