The only thing remotely close to a valid reason is that the 330 comes with more standard features thus is a better value than the 325, good luck with that. Honestly there are no valid reasons why you should get a 330 over a 325.
Since your parents are buying the car for you, you really have no say in the decision. Sorry if that sounds mean, but it's the truth. You should be happy enough that they are buying you a BMW.
My friend's lil brother is trying to convince his parents to buy a manual transmission Scion tC for him instead of an automatic, and he's even paying for the car himself every month he's just not old enough to take out the loan himself. That's a much different case since he's paying for everything himself, but even that might not go through.