“I did have a say in the decision…” That compounds the problem.
It is possible there was more going on than favoritism by other teachers. The district may have guidelines. The math teachers and GC may have an idea which students have the stronger skill sets, actively participate on a high level, more quickly grasp increasing challenge, etc, regardless of your class grades. We don’t know your situation.
But yes, strong math and science, rigorous course choices, and more, is key to getting into one of the premier STEM colleges in the country. It’s not all it takes, but this matters.
Now that you agreed to this path, your focus needs to be on how to resolve the issue it creates. You will need to supplement, one way or another, maybe use summer sessions to get ahead, look into local college courses or Dual Enrollment, etc. (Make sure your hs allows this, before counting on it.) Have that frank talk with the GC, maybe also the teachers, to get an idea if you are considered a strong stem kid. It’s more than grades.
And read the MIT admisions blogs. Before you set a notion of any dream school, make sure you know what matters to them, in building a class.