Using number variables

Hi,

Have spent a challenging day getting my head round the variables section of Storyline and am pleased with the result. However I am having an issue.

I have a fun assessment of 10 questions.  And depending on whether or not they get the question correct, determines whether they pass through a maze...ultimately to become a superhero in the subject. 

I have created a new variable called 'Choice', and when they select the correct answer, it adds one point to their score, and an incorrect answer adds nothing to their score.  Then I have added my own submit button which takes them to the right response (another screen) based on their score.  All very well in theory but if they click an answer (multiple choice) and then change their mind several times, I have found that each click of the correct answer adds a point to their score.  This is a problem as my submit button moves them to the screen dependent on their score.  If they are scoring more than they should for one question, based on clicking around, then the interaction gets stuck and doesn't move on.

Any suggestions on how to set it so they can't change their mind once they have clicked?  Or how the score can't go beyond 1 point in any question???? 

(I followed this tutorial: 

http://community.articulate.com/tutorials/products/adding-number-variables.aspx

)

thanks