I made a mistake like that also when I did a bargello with my MIL. We didn't see it until after it was completely hand quilted. It was quite upsetting for both of us, and we weren't happy until I tore out those sections, reverse appliqued them back in, and replaced the hand quilting. It is so easy to miss sections like that when all these patches and colors are vying for your attention! Congratulations on completing your quilt!!