You may have your QCW frame and leveling feet by now, but for others I will say get the leveling feet so you can level the frame precisely.
I leveled my Kreg table to within 1/32" (.031"). Then assembled the QCW frame on top of that and used my Nikon Total Station to adjust the leveling feet and bring all four corners within 0.010". From there leveling the wasteboard surface should be easy.
I wish the leveling feet had half-height lock nuts or there was a grub screw you could tighten to lock the foot adjustment in once you have it dialed in. If you slide the whole machine around on your table top you could inadvertently rotate one or more feet and given the coarse thread (I’m guessing the screws are 1/2"-13 thread) on the leveling feet a quarter turn is probably ~0.15".