It sounds like from your first post you haven't had much experience with benzo's... and so if they haven't ever been a problem, then I don't see why you should have to start over.
Yes you shouldn't of taken a prescription drug not prescribed, but you didn't really know what it was. Now you know, don't do it again, but don't throw away your previous sobriety time for a mistake that was not intentional 'using'.
Just my thoughts.