Hello Laura,
There a few ways you can fix that. You can add the widget back first and it will occupy the space there. This will open up more of the background image.
Usually, this blocked background happens as a result of the widget being deleted. The space occupied by the widget essentially collapses.
The code you showed up in your screen shot should work as far as adding more space. But, if you add the widget later, you may have more head room that intended. So, I would advise adding a widget there first and see if that gets you more space back.
Best,
Christopher M.