Wasteboard or gantry problem during assembly? Checking before I start belting and wiring

I assembled the gantry and went to put it on the wasteboard rails. It wasn’t fitting by just a smidge. Loosening the screws on the end plates just a tiny bit got it to fit but under the wasteboard on the cross bar extrusion I’ve got a small gap when it’s squared up using the corner brackets. Wheel movement is fine and all pieces touch/screw into each other as directed it just seemed odd considering how precise the rest of the parts are that these two extrusions would be off (maybe 1/2mm…saw blade width like someone cut on the wrong side of their mark)