Oh dear. Hours of work have just hit the garbage.
I made a prototype which was perfect. So what happened? Well I added an interfacing but that on it's own should not have caused this failure. I think the killer was asking my husband to clean up the pattern for me. He has made it look nice but shaved a few millimetres off the size. That together with the interfacing makes this design a failure.
Oh well back to the drawing board and I will do the drawing myself this time.