Limit quiz to once only in Storyline

HI

I am trying to limit the user to being able to only take a quiz with in my presentation only once.  I thought that by adding a variable on the results slide  would do it but i guess i must be missing something.  I am also posting this to our Skillport LMS system... 

the var is to add 1 everytime the failed slide shows but i'm not doing something correct because the user can just start the program again.  Can someone help out this green newbie

Thanks!!

Christina