Problem with PlayerPrefs

Hey guys, so I want to store the current score of my Pong game with PlayerPrefs so that I can load the scene (after a goal) again and display the score. But somehow it just gives my 0:0 everytime someone makes a goal. Maybe someone can help me.

Ball Script (OnCollisionEnter2D is important)

 using UnityEngine;
 
 public class Ball : MonoBehaviour {
 
     public float startSpeed;
     public float collisionSpeedMultiplier;
     public GameManager gm;
 
     private Rigidbody2D rb;
 
     void Awake () 
     {    
         gm = Camera.main.GetComponent<GameManager> ();
         rb = GetComponent<Rigidbody2D> ();
 
         float angle = Random.Range (120f, 240f) + Random.Range (0f, 2f) * 180f;
         float radAngle = angle * Mathf.Deg2Rad;
 
         Vector2 startDir = new Vector2 (Mathf.Cos (radAngle), Mathf.Sin (radAngle));
         rb.velocity = startDir * startSpeed;
     }
 
     void OnCollisionEnter2D (Collision2D col)
     {
         rb.AddForce (rb.velocity.normalized * collisionSpeedMultiplier, ForceMode2D.Impulse);
 
         if (col.gameObject.CompareTag ("TriggerRight")) {
             PlayerPrefs.SetInt ("pointsP1", gm.pointsP1++);
             gm.GoalPoint ();
 
         } else if (col.gameObject.CompareTag ("TriggerLeft")) {
             PlayerPrefs.SetInt ("pointsP2", gm.pointsP2++);
             gm.GoalPoint ();
         }
     }
 }

GameManager Script:

 using UnityEngine;
 using UnityEngine.SceneManagement;
 using UnityEngine.UI;
 
 public class GameManager : MonoBehaviour {
 
     [SerializeField]
     public int pointsP1;
     [SerializeField]
     public int pointsP2;
 
     public Text score;
 
     void Start ()
     {
         pointsP1 = PlayerPrefs.GetInt ("pointsP1");
         pointsP2 = PlayerPrefs.GetInt ("pointsP2");
 
         Debug.Log (pointsP1 + ":" + pointsP2);
 
         score.text = pointsP1 + ":" + pointsP2;
     }
 
     public void GoalPoint ()
     {
         SceneManager.LoadScene (SceneManager.GetActiveScene ().buildIndex);
     }
 }