Only two days after her lively appearance on Monday night’s American Music Awards, Britney Spears is making news about her upcoming big-screen debut. The former Mouseketeer, 19, will star in an as-yet untitled coming-of-age story to be directed by Tamra Davis that will start shooting in March, says the Hollywood Reporter. (Davis’s credits include 1995’s “Billy Madison,” with Adam Sandler.) Spears’s record company, Jive Records, will co-finance and produce the $10 million project, according to the trade paper, which describes the picture as “Boys on the Side” meets “Duets” — about three childhood pals: a straight-A student (Spears), a cheerleader and a burnout. While traveling across country together, they hook up with a would-be musician who persuades them to head toward Los Angeles for a music contest. No other casting has been announced. In other news of the “Oops! . . . I Did It Again” girl, the pop star topped the annual list of worst dressed women, announced yesterday by self-appointed fashion guru Mr. Blackwell. “Oops, she did it again,” proclaimed Blackwell in his trademark nasal delivery. “Her bra-topped collection of Madonna rejects are pure fashion overkill.” Britney was joined on the list by, among others, Madonna herself, Angelina Jolie, Bj rk, Christina Aguilera and Florida Secretary of State Katherine Harris.