How sure are you that you will get that score?? I mean is it a realistic goal, because if it is... chances are that you won't need that back up.
Here's a simple exercie
If you fail life... and get ....50 what would you do?
yes everyone needs a 'failing life plan'
Secondly work up... okay you didn't fail life... you got 70... is that enough to get into your coure? What would that get you into that you could transfer across into the course you want to be in? A science/art degree at a lower uni perhaps?
Then just go up and up until you get to your score.
Look by not putting something in the extra prefercences you are tempting fate my friend... don't give fate a chance... she's a bitch.