Hey, I was able to change my background! Thank you, Sandra, for figuring out what I was doing wrong! You can see that I uploaded a new drawing to work with.
Here is my finished sunflower. I was never able to change the background color despite restarting with a new file four times. Each time I got to the part to choose the paintbucket tool and change the background, my cursor would change from an arrow to a "no" symbol! I could not figure out why!