High Score not working - Quiz Game

Hi,

I am following this tutorial: https://unity3d.com/learn/tutorials/topics/scripting/high-score-playerprefs

However, my highscore is not adding up properly. At the end, it's always a fix number 280 for some reason.

Can show code on request.

If anyone can help, it would very useful.

Code (GameController):

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 using UnityEngine.SceneManagement;
 using System.Collections.Generic;
 
 public class GameController : MonoBehaviour
 {
 
 
     public Text questionDisplayText;
     public Text scoreDisplayText;
     public Text timeRemainingDisplayText;
     public SimpleObjectPool answerButtonObjectPool;
     public Transform answerButtonParent;
     public GameObject questionDisplay;
     public GameObject roundEndDisplay;
     public Text highScoreDisplay;
 
     private DataController dataController;
     private RoundData currentRoundData;
     private QuestionData[] questionPool;
 
     private bool isRoundActive;
     private float timeRemaining;
     private int questionIndex;
     private int playerScore;
     public Image answerImageDisplay;
     private List<GameObject> answerButtonGameObjects = new List<GameObject>();
 
     // Use this for initialization
     void Start()
     {
         dataController = FindObjectOfType<DataController>();
         currentRoundData = dataController.GetCurrentRoundData();
         questionPool = currentRoundData.questions;
         timeRemaining = currentRoundData.timeLimitInSeconds;
         UpdateTimeRemainingDisplay();
 
 
         playerScore = 0;
         questionIndex = 0;
 
         ShowQuestion();
         isRoundActive = true;
 
     }
 
     // Update is called once per frame
     void Update()
     {
         if (isRoundActive)
         {
             timeRemaining -= Time.deltaTime;
             UpdateTimeRemainingDisplay();
 
             if (timeRemaining <= 0f)
             {
                 EndRound();
             }
 
         }
     }
 
     private void ShowQuestion()
     {
         RemoveAnswerButtons();
         QuestionData questionData = questionPool[questionIndex];
         questionDisplayText.text = questionData.questionText;
 
         for (int i = 0; i < questionData.answers.Length; i++)
         {
             GameObject answerButtonGameObject = answerButtonObjectPool.GetObject();
             answerButtonGameObjects.Add(answerButtonGameObject);
             answerButtonGameObject.transform.SetParent(answerButtonParent);
             answerButtonGameObject.transform.localScale = Vector3.one;
 
             AnswerButton answerButton = answerButtonGameObject.GetComponent<AnswerButton>();
             answerButton.Setup(questionData.answers[i]);
         }
     }
 
     private void RemoveAnswerButtons()
     {
         while (answerButtonGameObjects.Count > 0)
         {
             answerButtonObjectPool.ReturnObject(answerButtonGameObjects[0]);
             answerButtonGameObjects.RemoveAt(0);
         }
     }
 
     public void AnswerButtonClicked(bool isCorrect)
     {
         if (isCorrect)
         {
             playerScore += currentRoundData.pointsAddedForCorrectAnswer;
             scoreDisplayText.text = "Score: " + playerScore.ToString();
         }
 
         if (questionPool.Length > questionIndex + 1)
         {
             questionIndex++;
             ShowQuestion();
         }
         else
         {
             EndRound();
         }
 
     }
 
     private void UpdateTimeRemainingDisplay()
     {
         timeRemainingDisplayText.text = "Time: " + Mathf.Round(timeRemaining).ToString();
     }
 
     public void EndRound()
     {
         isRoundActive = false;
 
         dataController.SubmitNewPlayerScore(playerScore);
         highScoreDisplay.text = dataController.GetHighestPlayerScore().ToString();
 
         questionDisplay.SetActive(false);
         roundEndDisplay.SetActive(true);
     }
 
     public void ReturnToMenu()
     {
         SceneManager.LoadScene("MenuScreen");
     }
 }

DataController:

 using UnityEngine;
 using System.Collections;
 using UnityEngine.SceneManagement;
 
 public class DataController : MonoBehaviour 
 {
     public RoundData[] allRoundData;
     private PlayerProgress playerProgress;
 
     // Use this for initialization
     void Start ()  
     {
         DontDestroyOnLoad (gameObject);
 
         LoadPlayerProgress();
 
         SceneManager.LoadScene ("MenuScreen");
     }
 
     public RoundData GetCurrentRoundData()
     {
         return allRoundData [0];
     }
 
     public void SubmitNewPlayerScore(int newScore)
     {
         // If newScore is greater than playerProgress.highestScore, update playerProgress with the new value and call SavePlayerProgress()
         if (newScore > playerProgress.highestScore)
         {
             playerProgress.highestScore = newScore;
             SavePlayerProgress();
         }
     }
 
     public int GetHighestPlayerScore()
     {
         return playerProgress.highestScore;
     }
 
     // This function could be extended easily to handle any additional data we wanted to store in our PlayerProgress object
     private void LoadPlayerProgress()
     {
         // Create a new PlayerProgress object
         playerProgress = new PlayerProgress();
 
         // If PlayerPrefs contains a key called "highestScore", set the value of playerProgress.highestScore using the value associated with that key
         if (PlayerPrefs.HasKey("highestScore"))
         {
             playerProgress.highestScore = PlayerPrefs.GetInt("highestScore");
         }
     }
 
     // This function could be extended easily to handle any additional data we wanted to store in our PlayerProgress object
     private void SavePlayerProgress()
     {
         // Save the value playerProgress.highestScore to PlayerPrefs, with a key of "highestScore"
         PlayerPrefs.SetInt("highestScore", playerProgress.highestScore);
     }
 }

PlayerProgress:

     public class PlayerProgress
     {
         public int highestScore = 0;
     }