There are three issues:
You have copy-pasted the shape of the collision. You have the same resource for ball and walls.
Check out all objects of CollisionShape2d node - shape resource. You can make unique. Right click on shape.
2, The position of the collision shape is at 0,0 position instead of the actual position of the sprite. Far away from the walls.
3, The collider shape size is very small too.