At the age of 14, your body is going through a lot of changes on your way to adulthood.
Bodies come in different heights, shapes, and sizes so I don’t know what “slim” means to you and whether you are at a healthy weight to begin with, so it’s hard to advise you specifically. My best advice for you would be to eat a variety of healthy foods. Running is fine, but it would be cool if you could do things that make your body move in a variety of directions.
I don’t know what hanging is, but if you’re hanging from something to get taller, it won’t work.
What do you intend to do with the exercise band?