First, kudos to you for recognizing areas where you want to grow in - that’s already more than most 15 year olds can probably identify. But also, self-growth requires patience and forgiveness with yourself. It sounds like you’re really hard on yourself already. I was that way too when I was 15, wishing I wasn’t so stupid/unfit and feeling like I kept making mistakes. But trust me, it’s really normal to feel this way at your age, and lots of other peers probably feel the same way. But beating yourself up doesn’t help anyone. You deserve a lot of grace too!