thanks a lot to all of you.
You sew one side with the long side of the pinwheel with the background fabric (3 layers) with the folded part of the pinwheel plus background (5 layers) and end up with..........just a lot :lol:
With the "flat" pinwheel it works well it is just the amount of layers with the 3 D one. Folding the seamallowence apart doesnt work as I will later quilt in the ditch and in that case I would just go over the thread.
I am not so afraid of the blocks coming apart but getting really stiff.