It seems like you haven't extended the lines for most of the boxes which is an integral part of the excersise.

What I can say about the pages which actually have had the lines extended, is that a lot of them are already pretty good.

A bit of advice that worked for me was to try and visualize how the face of the box you are making a line for would end up looking, and trying to think about whether opposite faces of the box would look consistent (their proportions stay more or less the same).