I learned to make sure that the right pieces are in the right places. I managed to put to swap the two shorter pieces on the 'T' on both sides. I didn't notice until it came to fitting it to the top and bottom. I've also taken the decision to sew by machine first and then finish with the over locker, it will allow for more precise sewing and add extra strength to the seams.
After all the fabric samples have arrived, I'll be packing this off to France where it can be tested. The feedback and photos will help me to make any adjustments before I start on the expensive fabric. Hopefully, it will only be minor adjustments that are needed.