There are old building tricks that will get you where you want to go. The plans call for 2 degrees or 2 and 1/16 inches total dihedral. I am presuming you haven't joined the lower wings halves yet. The LW12 clamp the spar between them to set the angle. You can set your root rib angle by propping each wing tip up to the desired angle 1 and 1/32 inches and then using a square to set the rib at vertical. glue it in place and trim any projecting spar material. This will allow the wings to meet at the desired angle. I have heard of Royal kits as being a case of carve and sand away wood until it looks like the desired airplane. In this case you will set the dihedral angle by measuring the wing tip height as shown on the plans and then trim off any projecting LW12 material until it is flush with the spar. Dry fit everything before you commit to epoxying the wing halves together and be careful that you don't introduce any twist into the wing, It may be necessary to trim F4A and build the wing with a single dowel rather than two dowels in which case you could also add extra material to the center ribs to give material to drill into.