Not what you want to hear.... but nylon does relax when wet. If I ever did another I would probably sew it on wet so that it was relaxed. A lot of work but you have the chance to remove your stitching and 'fix' it before you coat.

I switched to polyester because I hated that after all my hard work nylon would always go limp on the water. I have never used Goop but does it do like other finishes and loosen up when wet?