I can’t fullscreen in windowed mode without having a gap on the right side of my monitor. For example. in the moment it goes fullscreen in windowed mode, it shrinks to another resolution and i don’t know why. I have an 1920x1080 monitor.
I have the same issue, and have been for a long time now.
The only way to get it to scale correctly, is to go to the options and switch full screen mode on, and then off again. If I make the window “full screen” after that it scales properly.
Maybe it works for you too.
But it would be nice if it worked correctly off the bat so maybe Blizzard can look into this - after they sort out the patch-mess that is going on?
By the way: I have experienced this problem on several different hardware configurations with different mainboards, CPU, GPU, RAM etc. So it seems unlikely to be hardware related.