I would block it, especially since you haven't squared it up yet. Spritz some water on it, just enough to make it damp, and work out the wrinkles as best you can with your hands. Get it as squared and straight as you can, then stick rust-proof pins in the corners and edges through to the carpet and let dry. Then square the top.
p.s. I'd leave the bottom 2 rows on, I think they're fine! Or, remove the bottom row and attach it to the top. That will help balance it and I don't think ANYONE will notice the darkness at all.
eta: just realized you asked for help in squaring. Here's how I do mine, for the most part. I take a square 12.5" ruler, align it at each corner, and trim all corners first. Then I get my 36" long architect's ruler, fold the quilt in half (making sure to match the trimmed corners carefully), align the ruler with the cuts I just made, and trim the centers of the quilt.