ignore the resolution reported in-game. unless you have one of the commonly used screen resolutions, it will default to 800x600. (using the 1-to-1 while full screen will most likely hit one of the standard resolutions)

if the resolution was incorrect, your aspect ratio would be incorrect. this would mean the minimap would be an egg or football, instead of a circle.

also, make sure wow-menu/video/resolution/use-UI-scale is CHECKED.