I measured mine by setting one wing flat on the table and then measured the distance from the table to the main spar at the last rib using the wooden gage provided with the kit. It was right on the money but it looked like a whole bunch, so I sanded the ribs at the wing joint until I got it down below 3".

I have been flying the plane for several months now and if I had to do it over again I would take out even more! I'm sure your plane will fly with 5 1/2" but this is a whole lot more than you need. If you haven't glued the wings together yet then I would work on the joint and get it down at least to the 3 3/4" spec.