At the moment I am trying to get unity to run across 2 monitors. I've done some research and know that this is, strictly, possible. There is a workaround where you basically have to fluff your window size in order to get unity to render across both monitors.

What I've done is create a new custom screen resolution that takes in the width of both of my monitors, as seen in the following image, its the 3840 x 1080:

How ever, when I go to run my unity game exe that size isn't available. All I get is the following:

My custom size should be at the very bottom, but isn't. Is there something I haven't done, or missed, that will get unity to take in my custom screen size when it comes to running my game through its exe?

Oddly enough, inside the unity editor, my custom screen size is picked up and I can have it set to that in my game window:

Is there something that I have forgotten to do when I build and run the game from the file menu? Has someone ever beaten this issue before?