When the background of a diagram doesn’t match the size of the foreground page or pages, remove the background and assign a new one.
Remove the mismatched background. Click Design > Backgrounds > No Background.
Click Design > Backgrounds, and click the style you want. Even if it’s the same background style as before, assigning it again should match up the sizes.
Why does this size mismatch happen? It’s usually because one background page is shared by multiple pages in a drawing. The background takes the size of the largest diagram in those pages, and uses that size with each foreground page.
Multiple pages can use the same background image, but it’s best to give each drawing page its own background page, using the procedure above.
To find out more about backgrounds, see Add a background or watermark.