How do I activate Level 3?

Questions & Answers
1

I am making a 2d game in Unity and I have 2 Levels so far and it works but when I add a 3rd scene (Level) into the build settings, I can only play Level 1 over and over again. When I remove Level 3, I can play Level 1 and 2.

Here is the code for my finish line

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;

public class FinishLine : MonoBehaviour
{

private void OnTriggerEnter2D(Collider2D collision)
{

if (collision.tag =="Player")
{
    SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex + 1);
}

}

}

2

I put the levels like this in the build settings

lv1
lv2
lv3

if I am in scene 1 it plays lv1 over and over again
if I am in scene 2 nothing happens
and if I am in scene 3 I play lv3 first then lv1 and then lv3 again