Solved Problem with EntityDamage..

Hi guys, the problem is that while the world works but I want a world one and not the all.
#SorryForMyBadEnglish

PHP:

    public function onDamage(EntityDamageEvent $event){
      $player = $event->getEntity();
     if($player->getLevel()->getName() === "world"){
     if($player instanceof Player && $event->getCause() === EntityDamageEvent::CAUSE_PROJECTILE){
           $event->setDamage(2);
           $event->setKnockBack($event->getKnockBack() * 2);
           $sound = new LaunchSound($player);
           $player->getLevel()->addSound($sound);  
           }
        }
    }

I don't even know what you mean and what is the problem with your code..
What does "a world one and not the all" means ?

Solved... Please stop message