Recent Apps Button Not Working - Help

My "Recent Apps" button isn't working so I'm unable to use it in order to cycle through the apps I have open. When I hold down the button it says the following "Recent apps does not support split screen view". I know I accidentally turned on the split screen view somehow but now I can't find how to undo it. I think once I figure that out my "Recent Apps" button will work once more.

If anyone knows how to help with this problem I would appreciate it.

Thanks.