Steve,
I assume that the form in question is symetrical, fair on both sides of the centerline. Before you sand anything, loosen the errant form and shift it around a bit. you may have the form misaligned and moving it around may do the trick. You are looking for a fair curve along the sheer line,you might not see a small error, as long as the error won't compound as you strip the hull. Sandingone side may produce an uneven form, and the possibility of building in a curve.
Hope this helps. Have fun!
Steve