Flip the top plank of each pair of panels end for end so that both scarfs are at the same end of the planks. Pick a pair of planks and line them up so that their ends are together and their edges line up. When you are happy with the alignment, clamp the two planks together at both ends with spring clamps. Using long strokes with a sharp hand plane, remove any roughness or un-evenness in the plank edges. To keep from reducing the lap width too much, do not remove more than 1/16" of the plank's edge. If you will have to remove more than 1/16" to make the two planks the same, unclamp them and plane each seperately just enough to remove the un-evenness. This small difference in their shapes will not affect the final hull.