Like most of the top universities, Duke does not admit by major within its college of arts & sciences. In other words, it doesn’t matter whether you’re applying as a sociology or dance or chemistry major, and they don’t try to match extracurriculars with majors of interest. That said, Duke would like to increase student interest in earth & environmental science (e.g. they advertise for the major on posters in the campus buses), whereas the extremely high percentage of pre-meds at Duke makes biology one of the most popular majors on campus. I think a focus on Duke’s resources in this area could make a very good “Why Duke?” essay.
As for your stats, your grades and extracurriculars are in line for all of these schools, but your test scores - as you probably know - are a major weakness. If you can raise your SAT scores or score well on the ACT, you have a good shot.
I forgot to mention it earlier, but take a look at the New College of Florida. All admitted out-of-state students receive a $15,000 a year scholarship, which knocks tuition + room/board down to about $24,000 a year. It’s an excellent school for the natural sciences.