You can resize any background image to fill the background space at 100% of the width of your image - or more.
If you want to resize, you can click and drag the sides of the image or use the slider in the editing tools on the left. You’ll see the percentage change as you adjust the size.
When you increase over 100%, you'll see a warning indicating images over 100% may be pixelated but you are still able to use them if you'd like to.