You have to infect all of the lockers in the area to unlock next area. Choose an empty locker and then infect it. I forgot what key to push, but it should appear when you choose an empty locker. About the tattling, the number will go down naturally even if there are new reports about you, just make sure to play it safe when the number is close to the limit. Trapping guards and teachers can help. If you can upgrade your locker into the one that will trap the girl for the entire round, it's best to put guards and teachers there as their report point is much higher.