There should be little cards left in your stateroom showing the amount of stateroom credit.
The incentive stateroom credits (given by
DCL and the TA) are depleted first, followed by any stateroom credits that are purchased for you or by you as gifts. (I'm buying DH stateroom credits for each holiday 'til cruise time.) THEN the remaining balance is charged to your credit card. You can stop by guest services at any time to add cash or Disney Reward Dollars or even Disney Dollars to your stateroom account. If you do that, those dollars get used after the incentive credits and before the purchased credits.
Now I just gave myself a headache thinking about it.
As for charging your card, I believe they only do that at the end of the cruise. I usually let my CC company know that I'll be travelling and to expect a charge for stateroom expenses.