How to register single click to cause code to run?

The below code is on a When Drawing event.

I'm trying to make it so when you click my +1 actor button, it runs the code (Checks to see if capsules exists and if not, sets capsules to 1. Otherwise if capsules exists, set capsules to current-value-of-capsules +1.) When I set it to Mouse Was Pressed On Self, nothing happens. The number doesn't show at all. If I set it to Mouse Is Down On, the number shows and runs up the count for as long as I click and hold the actor. I just need to register a single click to cause a single +1 to be added to the value of capsules. What am I doing wrong?

Remove your "mouse is pressed on self" from the drawing event.
Use a mouse event that only changes your game attribute.

But I also need the number to permanently display to the left of the +1 actor button. What then?

Same thing. Drawing your value and increasing your value are two different things, handled by two different events.