Fold the corner over to get a 7.5" square.
Cut excess off.
Fold diagonally the other direction.
Fold in half length wise, and then again width wise.
Off set the corners, matching the length and width folds with diagonal folds.
Fold the corners down.
Cut the corners off, and now you an octagon.
Make sure you have 16 segments, you may need to half some of the larger segments if you do not have 16.
Fold up a section of four segments matching to the angles.
Open up and do the same to the other octagon points.
Looks the same but you will see triangles in the center this time of the framed area.
Fold down on the line.
Repeat folding down the triangles around.