put an image into 3 parts

[Nickd12]

So I was able to get it working the only problem is that when in full screen mode there are these white borders on the side so the image does not take up the full screen when in full screen mode. now ive done some research and I guess this is an OpenCV bug or something. I have found that there are some solutions on a windows pc but I have not found solutions for Macs does anyone have any ideas or any solutions that they know of?