I am truly in awe of you young people that are able to accomplish such great things so early in life.
It doesn't matter which school you end up going to, I'm sure you will accomplish great things.
Doing extra-curricular activities in your last year won't do much in my opinion. Being a club president for 3 months won't achieve that.
In the common app you have to write how many years, weeks per year, and hours per week you participated in your activity.
Duke is not Harvard but it's not that different. You need something that the admission officer looking though the stack, exhausted at 1 AM, remembers you.
I can't say anything about your chances because you've said very little but I don't believe purely having high scores will get you anywhere in the top 20.
Not to act like my username but getting admitted to Duke is no joke.
I'm not sure about Duke specifically but since it's a Ivy magnitude school, I assume that the application review processes is quite similar.
Elon is less selective but with your GPA Elon would love to have you.
UNC Chapel Hill is one of the best public schools to get into, but they are really harsh on out of state students.