Unfortunately while you have inventory items for use, their use is random. E.g., you may have a color/design available to use in one challenge but you can't use it in another, even though you have uses left. Also within the same challenge, sometimes you cannot use a design color/fabric on more than one item, again even if you still have more uses on the item. Sometimes, inventory items available depend on, for example, what color you chose for the wall. It is very, very frustrating.