My SO used to get impatient with cooling cakes and had the same problem. After some effort she learned that 'completely cooled' meant room temperature, not still warm to the touch.
If you want to be positive, use a thermometer to check the cake in its center. It should be the same temperature as the room it's in.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan