You could use a triggered event with a second global variable, so on the ending collision event you'd use "System>Variables>Set Value" and it'd look something like "2nd variable = 1st variable". Your second variable isn't counting down as it was triggered once. There's a much better way of doing this though. You can set up a function that will decrement the main score as long as you are in a 'play' state. When you collide and finish the level, change the state of your game to 'end', and since this will stop the score from decrementing, you can apply the score just from the one variable wherever you'd like (high scores table, text/dialog box, database, etc.) Good luck!
Paul