Setup an action to count the amount of times someone clicks outside of a clickbox

Since you use a click box, this should be a non-responsive project.

Add another click box under the first one, which covers the whole slide. Set up the Success event of that bottom click box to increment that variable, and set the number of attempts to Infinite.

I used that same approach for this game:

http://blog.lilybiri.com/find-the-differences-game