On mine, I found that gluing the wing jigs together helped (not specified in the instructions). I also made 2 sand bags (1 gallon zip-lock bags about 1/2 full). One on each wing created sufficient pressure to hold the wings on the jigs and hold the jigs against the table while gluing the center bracing. Although its difficult to determine visually with a di-hedral wing, there does not appear to be any twist or warp.

Brad