Show some pics of the problem if you can but basically yes the root rib should be at 90 degrees to the leading edge since the Edge 540 has a straight leading edge with no taper. The root rib should also be at 90 degrees to your building board with the wing upside down. If you are not that far off the easiest way to fix would be to glue on a piece of balsa the size of the root rib over the root and then sand it carefully so that it is correct. Only use a piece of balsa the minumum required thickness to get the job done. Use a large flat sanding block and check often with a square and by placing the wing on the fuse until you are satisfied.