Do not panic. Most likely, you just failed to click that Save Changes button.

For instance, you need to click Save Changes for any changes you made to the page.

Or after you crop a photo, do not forget to click Apply Cropping.

Or if you add any special effects to your photo, do not forget to click Apply Effects button.

Or if you made any changes and would like to leave the photo editing screen, please click Save Changes and Exit.

Or after you re-arrange all the pages into a different order, the Save Changes button is right below the page listing box.

Or if you changed any of the book settings, the Save Changes button is also at the bottom of the screen.