I knew plenty of people that had excellent ASVAB scores and didn't get their first (or even second) choice (and yes ended up as a MM). I even knew one with a 99. Like everyone else on here has stated, the odds are against you. There is really no point to letting you have a choice (other than maybe if you are aptly qualified for more than one rate), the navy will stick you where they want you.
I would not worry too much about studying calculus and physics. The navy will teach you their way of doing this type of work, and you will not have the option to perform derivatives and integrals in your head. In power school is where you will briefly touch calculus, and you will hardly recognize it as being so (it's very brief and just the very very basics). That is also at least 4 months into your naval career, and you will have other things to worry about.
Don't worry too much about being physically ready for bootcamp either. If you are in decent shape (I was 220lbs when I joined, and things went fine for me) you will have more than enough preparation to pass any physical portion of bootcamp. You will do your fair share of physical activity to prepare yourself there anyways (if you can do roughly 50 pushups, 60 situps, and run a mile and a half under 13 minutes you can already pass the physical readiness test at the END of bootcamp).
I would say your only major concern is getting to the next level of your life, which would be shipping out for bootcamp. Talk to your recruiter about this, he or she will tell you what you need to know.