Your post has a number of views but no one has felt brave enough to answer yet, so I'll take the fall. Were you here I would make you tea and sit you down before I broke the hard news. But it's a virtual kitchen table, so let me just start by saying that it's a really beautiful sweater. I'm sorry for your result. How discouraging this must feel.
Now some sadness:
I think the actual sweater is beyond doctoring. Felting will ruin it before it fits, and there's no surgery to fix that wide a size gap that will preserve the details that made it worth knitting, so that's out too.
So my suggestion is (are you sitting down?) to give it away and/or try again. If you decide to either give it away or rip to reclaim the yarn, make sure you record all the details of your finished sweater and use that to inform your choices in the re-knit. Even if you can't face Little Wave again, how that yarn behaved is critical to your successful re-knit, regardless of the pattern. And can I ask sheepishly: Did you wash your swatch? A lot of yarns grow lengthwise and or widthwise (depending on the stitch pattern) when they get wet. The called for yarn, Shelter, is pretty stable in the blocking process in my experience. Maybe your yarn is not.
So I hope this didn't break your spirit. I hope you try again. I hope you get it right next time. I really do. Maybe this can be your progress thread? We can all cheer you on!