Step 2
Lay two strips, right sides together, one on top of the other, squaring up the corners. On the top strip, draw a 45 degree line in from one corner across the width of the fabric to the opposite edge. Machine-stitch down this line through both strips and cut away the excess fabric, then fold the strips back to create a mitred corner. Repeat, attaching strips to the free ends of the first two strips until all four border strips are joined together to create the frame.