Calling function to update variable from prefab script not working as intended

 public class Airplane_Mechanics : MonoBehaviour
 {
     [SerializeField] int speed = 1;
     [SerializeField] Game_script game_Script ;
     void Start()
     {
         game_Script = Game_script.FindObjectOfType<Game_script>();
     }
     
     private void FixedUpdate()
     {
         Sprite imageName;
         imageName = GetComponent<SpriteRenderer>().sprite;
 
         // Add score according to finished position
 
         if (imageName.name == "Plane_Option_2_red")
         {
             if (transform.position.y > 1080) //red territory 
             {
                 game_Script.Good_Termination();//Good Termination
             }
             if (transform.position.x > 1920) //blue territory
             {
                 game_Script.Bad_Termination(); //Bad Termination
             }

 public class Game_script : MonoBehaviour
 {
     public int score;
     void Update()
     {
         elapsedTime += Time.deltaTime;
         
         if (elapsedTime > spawnTime && addNewPlane == true)
         {
             elapsedTime = 0;
             Add_score();
             scoreText.text = "Score:" + score;
             Random_plane();
         }
         else
         {
             addNewPlane = true;
         }
         
     }
     public void Add_score()
     {
         score += 10;
     }
     public void Good_Termination()
     {
         score += 100;
     }
     public void Bad_Termination()
     {
         score -= 400;
     }
 }

I am trying to update score from a prefab script Airplane_Mechanics. the problem is that it is called multiple times and increments the score by -20000 or so each prefab that is created. how can i make sure its only called once. The Airplane_Mechanics script runs on multiple prefabs at runtime if that helps.

If the prefab script is removed the score is incremented correctly with time. Can you change a variable from different prefab scripts all running at once or should I reinvent the way I'm keeping track of the score.

Thanks.