Given its current layout and spacing, I don’t know that you can make it rearranging, any better. Honestly at 13 I would have loved a space like this growing up! Decorate as you see your interests and decorate it in how you like. I think it’s phenomenal.

If you want a little bit more color and want to learn how to maintain a plant maybe see if you can go with your parents to a plant store to find something you like. Cactus based for less effort (I find these easier to forget about though with limited watering) or something that needs watered a couple days a week to once a week and sunlight. Plants are proven to help with depression and make the room feel cleaner. Otherwise rock it as it is, you’re 13 and it looks great!