I would not undo and redo. This is a scrap quilt (and a very cute and fun one at that). It's not visibly wonky, and even if it were, it's not a big deal. Unless your intent is to frame it and put it on a museum wall, such a small variation from square is not a big issue. In my experience, even if you got it absolutely perfect before binding, if you use your quilts on a regular basis and wash them, within a few washes you would have a little bit of unevenness. Not an issue. If you wanted something perfectly square and flat and uniform, you'd buy a mattress cover from Sears.
RST