Do make sure you have good debounce on the buttons, or you might miss your reset! 
If it accidentally counts as two when you're at 20 or something, it'll be 22 pushes. That might have been what happened when you couldn't get it to work the first time, you could do an easy fix by using >= (greater than, or equal to) 21 rather than == (is equal to).
But regardless, if it has to be exactly 21 counts, debounce is a must! 