Im 13 what excise should I do to become stronger
This may be old fashioned.
But when I was your age what realy helped me getting stronger was to find out who I really was.
If we dont know who we are then out training and gaining will be worthless. We could end up being just phisically strong but we miss our real potential in life. And I hope you will find yours.
Your potential contains the code what you are designed for. Working outside of that is often very stressfull.
At your age I started to learn to play guitar and today I am a fair steady an crazy chord-progression-writing rhythm Gitarrist. Besides that I am thankfull that I could start to study mechanical engineering and today im writing my bachelor thesis.
I dont say that training and gaining strenth is bad. But it would be a shame if you would miss the things you are made for. In other words. It would be a shame if you miss the things that will make you happy.