Whats this witches movie name?? (another disney movie)?

ok, another old movie that came out early 90's. I don't know the actors name in this and remember bits and pieces of this movie as well. IT's about a girl (16yrs old) and she has an eye on one of the cute guys in school but pays no attention to her. so she windes up at this witches house who gives her a spell to use to get to him. ....... it's an amulet she wears around her neck..... she goes to the mery-go-round to say the ritual...... she suddenly gets prettier and...... geez this movie is so old I don't remember much. The old lady who gives her the spell plays in the excorsist movie she is short, fat, and has a soft voice..... I hope to get a name of this movie!!! I can't remeber any other details to the movie!!