You have been executing a plan for 2 weeks now. You are likely doing the same workouts on the same days. Now is the time to change things up so that your body doesn't adapt. Normally I don't recommend changing things up until 4 weeks, but because of the challenge you are going to change things up today!
How To Change
If your weight workout has you doing:
Starting today it will be:
You change things by inserting different exercises in place of the exercises you were already doing. You change things by switching up how you get your cardio. If you've been using mostly the treadmill it is time to change to another piece of equipment.