Drag and Drop Newbie

I just got Captivate 19.  I am attempting to set up a "drag and drop" "game."  Children will drag an image of a 5 gallon water bottle into a grid.  The question is "How much water do individuals use in one day?"

I have 20 water bottles and 20 grid boxes.  I've set it up so that children can drag a water bottle into any grid box.

My question, if children do not drag all 20 bottles into the grid, they receive a "Good guess!  But a person uses 100 gallons a day!"  If the child drags all 20 bottles, the success message does not work.  How do I get it to show the success message?

Thanks in advance!!