u/Any-Helicopter1438

I'm trying to create an pattern for an action back jacket, and I cannot figure out how to sew through all three layers in their folded orientation. Am I missing something obvious? I've tried every order of sewing operation I can think of.

https://preview.redd.it/kxv1t9tjd6zg1.png?width=1284&format=png&auto=webp&s=22e7501b497454a987b30d55cb287320f019692c