I just finished assembling a box-beam external strongback, a la KayakCraft. Although all of the individual pieces seemed straight before assembly, when they went together, the top edge of one side section wound up slightly concave. This happened on one side only. Judging from a stringline, I'd guess that the concave section is about 1/8" to 3/16" off of straight, at the center of its eight foot length.

I'm not expecting perfection, but how close is "close enough"? Would I be better off fixing this now, or should I just forge ahead, compensating for it in the form setup (ie. by shimming the bottoms of the form extensions)?