Can you show a screenshot of your course page with the editing turned on and that topic section where you can see the book only with editing turned on?
I am posting with and without editing on.
You seem to be using the '"Show only one section per page" course setting. This means that you see greyed out links to activities (like 'libro') but in order to see them you have to click the topic section title and it will display the activities. Watch this video and pay attention to the part from 2 minutes, where it demonstrates 'one section per page':
Yes! That was the problem. I attached how I left it so for future reference. Thank you so much, Mary!