Yup ... seam allowance issue. Looking at the width of each blade at the center circle I see that they do not all match on the 2nd plate. Measure them up and rip out the ones that are smaller or larger.
Before you sew them back together measure the seam allowance on at least 1/2 of the seams on the hand pieced plate and get an average. Now you'll need to adjust the needle position on your machine to get the same seam allowance after ironing. Do a few test seams to make sure before you start the blades.