I don't know for sure but I think someone said you move up the plans once you have only one stone to lose. I hope a CDC will come along soon to confirm, but that is ringing a bell with me from my own CD days.
Your Counsellor should be able to tell you. It's usually a good idea to slowly and gradually begin to add food this close to goal. You've done so well! The important thing now is to steadily move towards maintenance.