Everyone has their way to sew cornhole bags for maximum strength.
Back-stitch at the beginning and end of the sewing. Use a triple stretch stitch on your template mark from one side of the opening to the other.
On the outside of the straight stitch, you can do a zig-zag stitch. Keep just to the outside of the stitch without overlapping stitches for bag integrity (this is not always done but is good if you play every day and is not necessary for casual use).
When finished with stitching- trim at all four corners. Follow the picture for directions.