You have to have the points available to you in order to complete a reservation.
As others have mentioned, the least expensive option, if you are short, is to borrow. You can buy your contract for any amount you wish so if you know 327 is the number, get that or 330 to allow a few points for changes.
If you book at 11 months, are short, and don't want to borrow from the next year, then you can purchase up to 24 one time use points at the 7 month mark. If you are trying for a hard to get reservation, this may or may not help you out.
But, if you are talking such a small point difference, I would probably just borrow if adding on more isn't in the cars.
With 325 points, and being short 2 a year, it would take 150 years, well beyond the terms of your contract, before you ran out.