As long as you didn't have to put a credit card down for them, then you'll be fine. I regularly make reservations for 2 instead of 1 due to different tables opening up and haven't had a single problem.
Reducing the number at the podium is far easier than increasing!
However, as mentioned, if you have put a CC down for any of them that are still at 3, you're going to need to call Disney Dining and get the number adjusted, you can (and often will) be charged the cancellation/no show fee even for partial parties.