Hem or clean-finish raw edges of fabric. Beginning on one edge, fold over and press the hem to the desired width. Using a fabric marker, on the wrong side of the fabric draw a line flush with the raw edge. Repeat the process with the remaining edges. Using a fabric marker and a ruler, on the wrong side of the fabric draw a line joining the two marked points of the raw edges and the intersection point of the creased hem line. Fold two adjacent edges of the fabric right sides together (your fabric will be folded on a 45-degree angle).Sew along the marked angled line. Trim the seam allowance to 1/4" (5 mm), clip the corner and press the seam open. Repeat the above steps for remaining corners. Turn the hem to the right side and topstitch.