Crocheting

**warning** some of this will be "shop talk." Sorry to anyone who doesn't crochet!!

On Saturday, I found a pattern for a crocheted afghan that I thought would be fun and really pretty. So I took Jasmine to Hobby Lobby to pick out yarn so I could make her a blanket. It's another triple-thick one, using three strands of yarn at the same time with a HUGE hook (I think it's a P...15.5mm)
This is the first afghan I made in that style:

It's huge. And thick. It has big holes in the pattern, but it warms us beautifully. 

I liked the look of a new pattern I found online. 

 

But by mid-day Sunday, I knew something wasn't quite right.

Um, something was *very* not right.

I was about to rip it all out and start again, but decided it was the perfect dimensions for a...

CAPE! Which she's been begging me for for months now!!

Your wish is my command, Jasmine.

So the boring part (ignore if you don't crochet)
my question is: can you help me figure out if it was *my* fault or the pattern's?? I know where the problem happened, and the math works perfectly for me to be right on that. But I'm getting my brain all twisted up when I try to figure out whether I was following the pattern correctly or not.

the basic pattern was 8 rows of sc, then a row of:
1dc, skip next sc, [(3 dc in next sc) skip next two sc] repeat [] to near the end, and then end with a couple more dc.

First of all, I misread the directions. I was doing *1 dc, skip, (3dc in next sc) skip next two sc* all the way across. But does the math work out that that should have worked???

I started out with 80 chains. By the time I stopped, I had 32 stitches. I'd done the dc rows 4 times. I figured out, if there were 4 stitches in 5 spaces, the math works perfectly for it to get down from 80 to 32. But I can't figure out if that's what really happened.

Any thoughts??