why is my GUI script bugging other GUI scripts?

so, i have many different GUI scripts attatched to my player object, one of which makes the player shoot enemies. So, i kinda figured out a way to identify the enemy being shot and display the health bar of THAT particular gameObject, but this particularly bugs my other GUI (crosshair, own hp bar etc.) in the initial phase, after which things get normal.

heres the script, please help::

 using UnityEngine;
 using System.Collections;
 
 public class hit : MonoBehaviour {
     private RaycastHit shot = new RaycastHit();
 
     public GameObject enemy;
     public enemyHp enemyhp;
 
     void OnGUI () 
     {
 GUI.Box (new Rect(420,10, enemyhp.curHealth/enemyhp.maxHealth*300, 20),"Enemy Health");
     }
 
     void Start () 
     {
     
     }
     
     void Update () 
     {
         Vector3 dir = transform.TransformDirection(Vector3.forward);
         Vector3 pos1 = gameObject.transform.position;
         if (Input.GetButtonUp ("Fire1")) 
         {
             if (Physics.Raycast(pos1, dir, out shot, 20f)) 
             {    
                 enemyhp = shot.collider.gameObject.GetComponent<enemyHp> ();
                 enemyhp.curHealth = enemyhp.curHealth - 10;    
 
             }
         }
     }
 }
 

thanks all in advance :3