Making the cushion
Stitch seams with right sides facing and raw edges level, taking a 1cm seam allowance. Refer to the diagram to cut two pairs of borders from linen. Pin the borders together in pairs. Stitch one diagonal edge, starting and finishing 1cm from the straight edges.
Open out the borders. Pin together. Stitch the other diagonal edges, starting and finishing 1cm from the straight edges. Press all seams open.
Pin and stitch the short straight edges of the borders to the embroidered square, pivoting the seam at the corners. Press the seam toward the borders. On the right side, pin and tack the pompom trim to the upper edge of the border, placing the top of the pompoms 1.5cm below the raw edge and 2cm in from the side edges. Cut off the excess trim. Repeat on each edge of the border. Cut two 42 x 29cm rectangles for the back from linen. Press under 1cm then 1.5cm on one long edge of the backs. Stitch close to the inner pressed edges to hem the pieces.
With the outer edges level, pin the backs to the cushion front, overlapping the hemmed edges. Stitch the outer edge using a zipper foot. Clip the corners, turn right side out and insert the cushion pad.