Hey first of all I just want to say I think you've made an amazing decision..congratulations and good luck!
Secondly though you might feel a little anxious now, when your course actually commences, and things start falling into place you'll feel a whole lot better about your decision to the extent that you'll wonder what you would have ever done had you not taken it up - it always happens that way, because all things ultimately work out for the best.
I've taken a lot of decisions following my heart and my instinct too, and they have never failed me. You're going to have such a blast in MIT