I have often encountered a problem with aircraft when it comes to the trailing edge. I pre fold the leading edge and pre curve the upper surface and the fix down the internal structure. I then run in to problems when I get to joining the trailing edges. Sometimes I find the upper surface comes over too far and you get a white edge underneath or the upper surface is too small and you get a white edge on the top. If I pull them to line them up I get a twist in the wing, the only way to get around this is to trim the white edge back. What should I be doing?