Larry, my opinion is basically the opposite of horace315. I put a higher priority on the strength provided by the dihedral brace and the fit of the wing center joint than the wingtip measurement. That's why a measurement isn't provided in the instructions.

The strength of the center wing joint mainly depends on the dihedral brace making firm contact with the top and bottom spars. If you sand the brace to make the joint come together properly, then you are sacrificing strength. However, a good center joint is important too. You want the ribs and sheeting to meet tightly. That in itself doesn't provide a lot of strength, but adding the fiberglass tape will tie the panels together and add strength.

At this point, I would recommend cutting a new dihedral brace to match whatever angle your wing panels dictate for a tight joint at the center. Let me know if you need some plywood, I'll send it right out.