Thread a tapestry needle with yarn that matches the knitted fabric. Hold the two pieces parallel with the right sides of the fabric facing you and cast-on edge at the bottom. Loosely pin the pieces together. Insert the tapestry needle from back to front between the first two stitches, just above the cast-on stitch; pull the yarn through, leaving a 3-inch tail. Insert the needle from front to back between the first stitch and second stitches of the second piece and pull the yarn through. Return to the first piece and insert the needle from the right side to wrong side where the yarn previously came out of the piece. Slip the needle upward under the next horizontal bar and bring the needle through to the right side. Cross to the other side and repeat the same process, going down where you came out, under one bar and up. Continue until seam is complete, pulling seam closed every inch or so. Weave in the tail. Use the beginning tail to even-up the lower edge by working a figure 8 between the cast-on stitches at the corners. Insert the threaded tapestry needle from front to back under both threads of the corner cast-on stitch on the edge opposite the tail, then into the same stitch on the first edge. Pull gently until the “8” fills the gap.