Well to be honest making art for your game isn't that easy & it'll take time to make nice backgrounds, this is not good especially when you're prototyping where you have to have a playable game as fast as possible, But don't worry & because I love you I have made you a 2D Backgrounds Pack that contains 7 different cool 4K high-resolution backgrounds for your game, I have used some of these backgrounds on my game & dude it looks so beautiful, the package contains PSD & Krita files of all the illustrations so you can edit them with your favorite photo editor, also it contains all the layers as png files, so you can make your game much nicer with these backgrounds.

Ultimate 2D Backgrounds Pack