Thanks. The problem is with the foundation edge not being stiff enough to hold the edge while I turn the fabric allowance under. I did try spray starching but the foundation still did not stiffen it up sufficiently. The foundation is semi-water soluble, so I had to be extra careful handling it while it was wet with the starch too.
I am going to do the same pieces with my old method of freezer paper and and children's paste to see if the results are better. It may be I choose pieces that are too tiny to really get a good test result on.