New Modular Wasteboard issues

I’ve been assembling the new modular wasteboard and I’ve been having problems with measurements as well as the backboard not fitting. I have taken apart and reassembled 2 times. The instructions say 1.25" overhang on the 1000mm extrusion, but if I follow this measurement the backboard holes don’t line up with the frame. What could I be doing wrong, and also how important is the overhang measurement? I don’t want to fight this later so I want it as perfect as it needs to be.

From the looks of it in the picture the panel front ends bolt to the front left to right extrusion. I don’t think it would have any impact except esthetics. The rear portion doesn’t get a router to go back that far in there.

My own machine has T slot and basswood and the front is uneven with no issues. Someday I might trim it off…LOL. .