It's unlikely that you'd be playing the part in a movie adaptation of your book. When you get your book adapted into a movie, it's like giving up your baby for adoption. The director may find your input useful but more likely they will find it restricting. You could direct it but you'd have to be very good at film directing. FILMS ARE NOT JUST BOOKS THAT MOVE. You can't literally translate a book into a film- you need to expand it and edit it so that it is a good film.
Sam Shepard played the male lead in the film of his play, Fool For Love, and he did it very well, but that's a play not a novel. He's used to having other people interpret the parts. You won't be.
EDIT- figureskate, there is no set interpretation of characters in plays or film. You should know that as an actress. If your book is good, your writer's intention should be obvious. And you'd end up interfering with other characters.