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scaling up to box size won't help, big cards with FFG sleeves are 93mm long, but there should be at least 1mm space extra to put them in, which is 94x3 = 282mm and there is 286mm space, that is 4mm for 4 walls. i'd probably make ~0.45-0.5mm (1 extrusion line) two inner walls each and 1.5mm for each outer walls on the sides. no need to change front and back.
also small cards are 67mm long so at least 68-69mm space would be required which could probably be achieved in simmilar fashion.

again simple scaling would mess up whole model as all the tokens would be too loose probably.

thickness of sleeved cards is also almost twice the unsleeved ones, but scaling in Y axis probably wouldn't mess the model that much... maybe

i could... probably make this from scratch using your work as a reference using fusion360 that i'm familiar with, but if you still have raw files it should be as easy as few clicks for you. (though i'm not familiar how it's done in sketchup, i might be wrong here)