Hola, Jorge! It looks as if you don’t have the auto layout constraints set for the game background to stretch to cover the whole screen. Check that you have set the auto layout constraints correctly as per the instructions in the book.
If that doesn’t help, check your project against the provided final project in the book since that can help you troubleshoot the issue yourself.
If you are still stuck, please upload your project as a ZIP file somewhere and provide a link to the ZIP file so that I (or someone else) can download the file and see what might be going on.