Carol,
It is hard to judge this without seeing a side to side reference.
The form seems well considered, however.
This is the classic way to get an understanding of forms and you should do more of them.
A good book to show you how to get into paint using casts is
"The Practice and Science of Drawing", by Harold Speed.
It also goes into painting monochromatic heads from life.
You can find it at the Strokes of Genius Art Book Store. Just click on the ad on the right, it is under drawings.