Why do you have “average course rigor” compared to your classmates?
The key to college acceptances is to find colleges that fit the academic profile you have…not wish that it was different. So…start looking for colleges that align with who you are.
Your private school counselor will surely be able to help. These folks want to see their school grads placed at the best colleges they can get accepted to. So…when the time comes…work with your school counselor to find colleges with very similar characteristics to Dartmouth…that might be more reasonably attainable.