What result do you get? Maybe post a screenshot.
You could try some extra css like the following:
background-repeat: no-repeat; background-attachment: fixed; background-size: cover; overflow-y: hidden; max-height: 100vh;
This will make sure the image covers the page while avoiding scrollbars when the scaled image is higher or wider than the screen.
Also, do you have enough content on the page to fill the screen? Otherwise set “height: 100%” on the body. Otherwise the image will fill the background of your page, but the page doesn’t fill the available space in your browser window and you still end up with white space at the bottom.