How do I know how many watering cans I have?

The game tallies up all you have earned from purchasing collection set items and only shows you how many more you need to reach the grand prize goal on the progress bar, located when you click on the collection set icon (watering can this month) on the bottom of your main scene. Note that the progress bar does not count up the items that you have purchased but are in construction. However, it does denote it in a darker color on the bar to let you know if you have enough to reach the goal after construction is complete.