kitchen window oops

i just created basic outlines of all windows and doors in sketchup, to get an idea of how they size up visually. then, i noticed there wasn't much space under the kitchen sink window. i measured downstairs - the countertops here top out at 36". plus space for backsplash, a good rough opening position would be 42". if the rough opening top is at 80" (which i assume the windows will all be at) then that window can only be 38" in height, not the 42" i spec'd. whoops.