Hello , I will like a little bit of help regarding a game that I create.

Idea is that I am pretty new in programming just as a hobby and my game have scrolling background. I have different scenes that I will like to add to my game play as If the player make a 50 score to create a pop up with a button that will launch the new scene but keeping also the score from the previous one. Also when my hero dies I will like to start the game on click with the initial scene and score to be again 0. I am loosing it and cannot do this to work proper.

-using UnityEngine;

-using System.Collections;

-using UnityEngine.UI;

-using UnityEngine.SceneManagement;

 public class GameControl : MonoBehaviour

{

 public static GameControl instance;            
 public Text scoreText;
 public Text highScoretext;                                                
 public GameObject gameOvertext;                                                
 private int score = 0;
 public string CongratulationsMenu;
 public bool gameOver = false;                                                
 public float scrollSpeed = -1.5f;

 void Start()
 {
     highScoretext.text = "High score: " + ((int)PlayerPrefs.GetFloat("HighScore")).ToString();
   //  score = PlayerPrefs.GetInt("Score");
 }

 void Awake()
 {
     
     if (instance == null)
                   
          instance = this;
      else if (instance != this)
       
         Destroy(gameObject);
 }
     
 void Update()
 {
     if (gameOver == true && Input.GetMouseButtonDown (0))
     {
      SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex);
     }
     if(score >= 3)
    {
         NewWorld();
     }
   //  scoreText.text = "Score: " + score; PlayerPrefs.SetInt("Score", score);
       }
   
 public void HeroScored()
 {
     //The bird can't score if the game is over.
     if (gameOver)
         return;
     //If the game is not over, increase the score...
     score++;
     //...and adjust the score text.
     scoreText.text = "Score: " + score.ToString();
        }
          public void HeroDied()
     {
     //Activate the game over text.
     gameOvertext.SetActive(true);
     //Set the game to be over.
     gameOver = true;
     if (PlayerPrefs.GetFloat("HighScore") < score)
     PlayerPrefs.SetFloat("HighScore", score);
        
      }
 public void NewWorld()
 {      
     Time.timeScale = 1f;
   //  PlayerPrefs.SetFloat("Score", score);
     PlayerPrefs.SetFloat("HighScore", score);
    //scoreText.text = "Score: " + score; PlayerPrefs.SetInt("Score", score);
     SceneManager.LoadScene(CongratulationsMenu);
  
 }

}

the commented code is some of what i have worked with, Could some of you that have experience may help me ? Thank you in advance.