This can happen as the balls are quite delicate but it’s OK – you can push in a pen or pencil (or blunt end of a knitting needle if you have one!) into the hole and push out the dent. If you are a perfectionist then you can spray a little water on the dent and push it into the perfect round shape. When it dries, hey presto, it will be perfect again (and you’ve saved the environment from posting spare balls back and forth and saved yourself a trip to the post office too!).