I liked Liz's suggestion of making a pillow. But my mom convinced me to try making the skirt again.
So first, I unpicked the entire thing. Then I put the zipper back in with the smallest seam possible. I did the smallest seams possible down the back and down the sides.
Then I unpicked the darts.
And it fit!
I decided that after all that, I was totally never going to try and put a hem in, and the pattern said to do the waistband with twill tape, so I just bought some bias tape and ran it around the waist and the hem.