I am affraid that when I continue with the other chapters and the weeks go by, I will forget the initial chapters.
Don't worry about this too much. The chapters are not independent: you usually need the knowledge from ch. 1 to understand ch. 2, and need 1+2 to understand 3. So to a large extent you are almost continuously being reminded of the theory in earlier chapters.
And you are making notes for yourself, so that you can revise quickly, are you?