First tack the bottom of the fuse to your work bench/building board to keep it flat. glue the joints at the rear of the wing making sure they are straight, then, work your way back one former at a time making sure easch one is straight. Once they are all glued, they will hold their shape. It is not necessary that they are straight in their relaxed state. Die-cutting will creat stresses on the wood that will cause those warps you are experiencing, the formers are what will straighten them out.