without the brace in do you get your clearances as per instructions at each wingtip? the dihedral brace can be sanded as long as you get your proper dihedral measurement at each wingtip. I have had the same problem with the braces and things off slightly off. instead of tearing the wings apart just adjust the dihedral brace to get the clearance you need and close the gap. those braces set the dihedral but don’t have to be an exact fit they add strength to the wing to help join it but it isn’t that critical as long as you get the proper dihedral as per instructions.