I found it hard to resist the temptation of overdipping. When I speed up scanning down through the center of the page, I hardly recongise anything.
That's perfectly normal. And it's why you have a mind probing question.
Is that:
First time: to notice the section you are interested in;
Secnd time: dip into the section ?
Each time it is to answer mind probing questions. You may look at the same page again when you have another question. So with truly active activation you're looking at the page more than once to answer questions. Look at page 60 of the 4th edition of the PhotoReading book and notice the authors train of thoughts. That helps you to connect with the way an author thinks when. So in one page or paragraph the author can, talk about a problem and explain why it is a problem. It depends only on your purpose.
Finally, I activated and mindmapped a book with 300 pages recently. Yet, I used 5 sheets of A4 for the mindmap. Am I doing too much?
by my estimation no you're not doing too much many will do a 300 page book on 2 or three A3 pages so working in a smaller format it's probable you would use twice as many.
The person to check in with is yourself. Would you like to do less next time? Or is that fine? How is it when you review the mind maps? Ultimately how useful are the mind maps to you?
AlexK