Happy 16th Birthday and congrats on getting to go to Japan!
I didn't spend too much time in Tokyo when I was in Japan, but I know that before I went, I looked at a bunch of guide books and found places I wanted to go. So, I just wanted to suggest that you check your local library for guide books of Japan or Tokyo
And if you can't figure out what to do, you could probably hang out in a train station for a few hours. I know I spent a bunch of time at the Shinagawa station and they have lots of stores and stairways and places to explore. Train stations also have police around if you aren't feeling safe being alone. And they're a good place to go if you like people watching. Some stations even have an underground shopping center, though I don't know how many of those are in Tokyo...
