Messed up.
 

Can you think of what I can do to fix this? Even if I pull the stitches out, I won't be able to quilt it so that it will look better, I don't think. And it all was going so well until now, and I was almost done :-(

One option I can see is Put on "Miracle on 34th street". Begin taking out the stitches and don't stop until the area of fullness can be reasonably flattened. Might have to unpick a square foot or more. Pin baste the heck out of it and requilt.
If this is the back, and the front looks OK, you could just leave it.

If this is the back put your label over this area.

It's not the back.

I've pulled stitches out of almost an entire quilt before. It doesn't take as long as you might think. I agree with PaperPrincess; chances are you can un-stitch enough so that you can flatten out that area.

I agree with Paper Princess, remove the quilting from at least a square foot, maybe even 18 inches, pin vigorously distributing the fullness across the entire area you have frogged, then quilt slowly over the area - starting in the center of the area (maybe follow your previous needle holes with a blue fabric marker so you don't lose the pattern) and leave the pins in until you absolutely MUST remove them. I quilt on a longarm, so I am basically telling you what I would do in a similar situation. You will end up with a little fullness spread out all over the area you picked out so it shouldn't be as noticeable.

Honestly, I would probably leave it in. Assuming it's cotton batting, it will crinkle once it's washed/dried a few times & won't be terribly noticeable. The lesson I've learned to prevent that problem is always, always, always to SITD the entire quilt before I start doing any of my FMQ. That way, any extra fullness will be pushed to the edges rather than getting trapped between stitching lines.

Unless you remove the pucker then it will always look like a pucker, not a crinkle. I go with the suggestion of removing the stitches until it smooths out.

Hmmm I think in this instance I'd sigh, grab a glass of wine, put my magnifying goggles on and unpick a good size area to redistribute the fullness. But perhaps I would wait a day or two first and then revisit it...sometimes things don't bother you as much after a bit of time.

Yes, to clarify: I meant the fabric will crinkle.