setBlock and getBlock, I need some help

Hi, I'm new to Pocketmine plugin development.
I'm creating a plugin for a minigame, so now i'm testing setBlock and getBlock.
With my script I want to create a platform with a different color of wool every 5 seconds
Here's my script:

PHP:

<?php

/*
__PocketMine Plugin__
name=Blocks
version=0.0.1
author=YoDevil
class=Blocks
apiversion=12
*/

class Blocks implements Plugin{
    private $api;
    public function __construct(ServerAPI $api, $server = false){
        $this->api = $api;
    }

    public function init(){
        $this->api->schedule(5*20, array($this, "timer"), array(), false);
    }

    public function __destruct(){

    }
   
    public function timer(){
        $wool_color = rand(1,15);
        $level = $this->api->level->get("blocks");
        for ($x = 1; $x <= 20; $x++) 
        {
            for ($z = 1; $z <= 20; $z++) 
            {
                $testforBlock = $level->getBlock(new Vector3($x,80,$z));
                if ($testforBlock->getID() === BlockAPI::get(0, 0))
                {
                    $wool_block = BlockAPI::get(35, $wool_color);
                    $level->setBlock(new Vector3($x,80,$z), $wool_block);
                }
            }
        }
    }
}


This code doesn't work, and I don't understand why. It looks ok for me, but I'm also new to PHP so maybe i can't really see my mistake.
I've tested and the blocks at height 80 are air blocks (line 34), so that is not the problem.
Please help me!
Thanks in advance

New api soon... Pointless you making this ._.

I recommend you to learn the new API, it easier to use, but a little bit hard to learn xD
http://docs.pocketmine.net

Ok thanks all!