This was hard to get a pic of to show what’s going on. I’m redoing a 91 bronco rear bench seat. The pattern is symmetrical from one half to the other. So I just made one set of patterns and reversed them. All the alignment marks everything are the same. On one side the seat cover lays down nice and smooth. But here on the opposite side it’s puckered up. Just to help me understand I stretched this way and that to see if it was a matter of adjusting and which way to lay flat. But nothing helps 100%. It’s only 4” of the total seam for the piece too.

To me, I think of taking a sheet of paper. Lay it flat on the table and put your hands on each side and move them with the edges of the paper together and it lifts in the middle. But for this, it’s just a small area with no tension pushing on it to lift it. I plan on taking it apart and redoing it, but for learning reasons I’m curious why it did this.