Just so you can see what it looks like pre-adjustments:
I'm wide, but not quite that wide at that spot. And you know how it is — you never want to look wider than you are; as wide as you are is PLENTY. So I think I'm going to try a ribbon through the ribbing (need to go buy some fabric ribbon first) as some of you suggested. And I'm definitely going to redo the buttonhole band. Somehow, even though I count the same # of rows on the left and the right fronts, I ended up having WAY too many stitches on the buttonhole band. And I tried cutting it down, but did the math wrong -- so it's still more stitches on the buttonhole band than the button band. That's only part of why it's gapping, but still -- having them the same would help. Then I might put some hooks on the back of the buttonhole band in between the buttons, to help smooth out the connection.
Yeah, I know I have one more button to sew on. I'm lazy.