If you're unsure then wait until you are totally sure before doing anything. If he doesn't like that answer, well tough shit. You're the one that has to live with the decision, not him.
Anything is possible. You do need good grades to get into pharmacy school. I don't know the exact requirements but you could find that out easily enough. As far as general chemistry, that wont be enough for pharmacy school. You'd need o-chem and probably physical chem classes as well.