Make sure you starch the heck out of the material before cutting (if you are not done cutting). Sometimes the bias on the HST can stretch.
Second - watch your seam allowance. I've had this same problem with this pattern and usually the seam went slightly "Wonky" in the area where the overage occurs. It only takes one or two threads width difference in the seam to add up to that amount of difference on the edge.
Love your use of the prints and the green trellis/twists.