Some of these private high schools have dedicated college admission counselors and privileged connections to elite private colleges, so you may want to ask those college admission counselors which, if any, elite private schools are realistic to apply to for you, and how extracurriculars can affect your applications there, since they may be able to give you better information that typical outsiders (including people on these forums and high school counselors at ordinary high schools). If that describes your high school, ask the college admissions counselors there.