Unfortunately, we cannot add to an order that has been already placed, but you are welcome to place a second order.
Note to group coordinators from Robyn: I personally order extra of popular items when I coordinate a group, because I always have people come to me after ordering closes. It’s up to you whether you want to risk having excess items. If you find yourself in that predicament, you can offer the leftover items to your group. As my group has grown, I’m able to take that risk because someone will always buy the extras.