I have found that seams that don't match perfectly or have the white edge showing can be cured with colored pencils. Since your background is black, try taking a black colored pencil and lightly go over the seam, even going on the paper around the seam is ok. Then wet your finger and using a swirling motion work the coloring into the seam. This takes it off the paper and puts it into the seam where you want it. Try a section that is not noticeable, just in case! I recently did this with a red background paper where I had some white spots showing from the primer on the wall. It worked quite well.