i did it on my own, i started with about 15 sts depending on the thickness of the yarn. then i increase i sts every row to a certain width then i start decreasing to the first part. Then till i get the size, i pick sts along the side and k2 p2 one round.
Actually, you can do a square shape and pickup sts. k2, p2 in smaller needle so it fit in better. Mine is alittle loose inside.