First, I actually used a long ruler to score where the long valley folds in step 81 are, rather than trying to fold a straight line with all the pleats.
Then I precreased everything, (which I assume you have done).
But what is basically happening, is (viewed from the stomach) you are creating a point, (where the two large mountain folds meet, that becomes the point), and then folding that point underneath. The zig-zag folds immeadiatly above the point are the result of the point being folded under, (the tip basically becomes the top of a water bomb base), which has been attempted to be shown in step 82.
Now that I'm looking at it, (I folded it a couple of years ago), I didn't directly follow the directions, I only folded the horizontal mountain and valley folds in the middle "column", and I just now realized that in step 81, step 80 has been partially folded, which explains the shrunken zig-zags (because you are looking at them from an angle).
As for compensating for the extra paper on the side from the long vertical valley folds, I did what was shown, just not to that extreme.
I also found it helpful to fold the vertical folds to keep the pleats from unfolding during the collapsing.
Anyway I hope this helps and its not too late! If you're still stuck, I can upload the photos of my head, in hopes of clarification.
Do you think you'll ever fold the whole thing? I did after folding the head twice(to make sure I knew how to fold it), and the paper stretched down my entire hallway!! O.O
Its after you make the crimp folds and then you have to collapse it. My paper just isn't doing what its supposed to do. Any help would be appreciated 
