You might want to experiment a little with the the proper length of elastic for your hair. Sew as far as you can, twisting the fabric out of the way as you sew. Turn right side out through the unstitched gap. Fold the seam allowance of the unstitched edge to the inside, and edge stitch the opening together from the right side, through all layers. Suggestions Experiment with other fabrics, and be aware the dimensions of the fabric piece you start out with will change with each type of fabric.
Heavier knits require smaller dimensions, and sheer fabrics require larger dimensions.
Do not allow it to hand over the edges of the table. Do not use pins to secure the pattern. Trim the excess paper along the cutting lines of the pattern, and use weights to keep the pattern from shifting around. Mark around the edges with chalk. Lift the pattern out of the way to mark notches and avoid using small nips in the edge to mark them.