I had a similar problem with a quilt for my Grandsons wedding. He is in the Air Force so I wanted to make a patriotic quilt for them. The red and blue bled onto the white on the back. I rewashed it with color catchers and the bleeding came out. I then washed it with salt and vinegar as I was told it would set the colors. The quilt turned out well. Good luck.
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The red and blue in the flag material bled all over the white on the back. This picture was taken after I got the bleeding out of the white.