Jesus, you've set a Windowed size of "3440 x 1332". No wonder you have so large left / right black borders. Your width is almost triple the height.
I can't display this properly on my laptop.
What is your computer / monitors maximum resolution?
If I change to "800 x 600" then it looks like this:
Also, under "Filters" you've got scaling set as "Default". Change this to "No scaling".
I think what you'd be best doing is setting "Fullscreen" and "Native". Then under "Filters" use the integer / display multipliers e.g. 2x.