Level Selector not working on build

Hi, Im having issues with my level selector scene, since I followed a Brackeys tutorial on how to do it, everything seems to work great on the game view in Unity but when I build the game all the 3 buttons for the levels are unlocked and accordingly to the scripts it supposes to be that the level 1 is unlocked as of course we want to start playing... Im having a hard time on this issue.... any help would be really appreciated

Thanks!

Here is the Brackeys tutorial https://www.youtube.com/watch?v=-cTgL9jhpUQ and the script that Im using

   using UnityEngine;
   using UnityEngine.UI;
   using UnityEngine.SceneManagement;

  public class level_selector : MonoBehaviour
  {
 public scene_fader fader;
 public Button [] levelButtons;

 void Start ()
 {
     int levelReached = PlayerPrefs.GetInt("levelReached", 1);

     for (int i = 0; i < levelButtons.Length; i++)
     {
         if (i + 1 > levelReached)
             levelButtons[i].interactable = false;
     }
 }

 public void Select (string levelName)
 {
     fader.FadeTo(levelName);
 }

}