It’s impossible to say given the information you supplied. However, I am hesitant to say you won’t get into all these places.
First, do you have any hooks? Seems like you are not a recruited athlete, but did you look at MIT’s stats? I don’t know about track, but MIT sports have gotten quite competitive.
Are you 1st gen? URM? These are huge at MIT. Do you need FinAid - MIT has a strong preference for applicants who need fin. aid.
You come from a small town in AL - that is a plus for MIT and a lot of colleges that want geographic diversity.
Yes, retake the SAT - maybe try the ACT. Also, you need the subject tests for us to figure out what you need. What math are you taking - are you sure you don’t want to take Math 2?
As far as nuclear engineering goes, there is not reason to not list this - if you have pertinent experience and strong reasons for saying nuclear engineering (are you considering ROTC and the military) then that will not hurt you. MIT wants a diversity of majors, so if you choice is genuine, it will only help.
I have thoughts on other schools, but won’t comment since this an MIT string.
Good luck.