Looks like Dartmouth enrolls about 50 native americans each year. Your ACT score looks fine. A 30 at age 15 is pretty darn good. However the GPA might need to be explained. Can your guidance counselor explain this in their letter? The 4.0 university GPA is a good sign though.
Dartmouth has been long known to attract native american students. Do you live on the reservation? Or if not, do you have any connections with family members from your dad’s side? This would be good to emphasize in the essays.
If you don’t get into Dartmouth ED, have you considered an ED2 school? Your profile will be a hot commodity, so there are likely many schools who would like to have you.