The reason the planks are different widths is so that they will ultimately take up all the space without the need for tapering. The downside of this is they must be precisely laid down (exactly like in the computer drawing) to the millimeter or you may end up with a gap. Even though I am a CAD/CNC/Laser guy I don't particularly care for pre-fabricated hull planking because it is nearly impossible for a human to build precisely to the drawing. I can already see very, very slight variances in the placement of your planks and you are only 2 strakes in. The overall "length" of your plank is not the primary concern - they are typically cut just a little bit long and need to be trimmed to fit into the rabbet - this is normal. Most likely your variances are appearing due to uneven fairing in of the frames/ribs. I notice most of them still have all the laser char. Ideally, all of the laser char would have been removed from the edges during the fairing in process..
Since it is a small model... the placement/positioning of these pre-fabricated planks becomes even more critical. In many ways, a larger model is easier to plank than a smaller one.
Hope this helps some.
