Health bar update

Hello,

I'm currently trying to add an Health bar to game and I'm having issues with updating its length. The bar itself is very basic, however whenever I alter the curHealth variable, the length of the Health bar isn't updated accordingly. For example, with a maxHealth of 100, the bar only updates when curHealth reaches values of for example, 50 or 35.

 using UnityEngine;
 using System.Collections;
 
 public class HealthAmmoBars : MonoBehaviour {
 
     GUIStyle shurStyle = new GUIStyle();
     public Font myFont;
     public int maxHealth = 100;
     public int curHealth = 100;
     public float healthBarLength;
     private int numShur;
     GUIStyle healthstyle = new GUIStyle();
     Texture2D texture;
 
     // Use this for initialization
     void Start () {
         shurStyle.font = myFont;
         shurStyle.normal.textColor = Color.white;
         healthBarLength = Screen.width / 4;
         //texture = new Texture2D (128, 128);
         //AssignTex(texture, red); 
     }
 
     // Assign color to a texture 
     void AssignTex (Texture2D tex, Color col){
 
         for (int y = 0; y < texture.height; ++y) {
             for (int x = 0; x < texture.width; ++x) {
                 texture.SetPixel (x, y, col);
             }
         }
         tex.Apply ();
     }
     
     void OnGUI() {
         
         // Shuriken bar
         string numShurProjStr = "Shurikens: " + numShur.ToString(); // Since its a static variable
         GUI.Label(new Rect(10, 50, 500, 100), numShurProjStr , shurStyle);
 
         // Health text
         GUI.Label(new Rect(10, 22, 500, 100), "Health" , shurStyle);
 
         // Health bar
         GUI.Box (new Rect (50, 20, Screen.width / 4 / (maxHealth / curHealth), 20), curHealth + "/" + maxHealth);
 
 
         //healthstyle.normal.background = texture;
         //GUI.Box(new Rect(10,10,Screen.width / 2, 20),"" ,healthstyle);
 
     }
 
     public void UpdateHealth(int adj){
         curHealth += adj;
 
         // HP cannot below 0
         if (curHealth < 0)
             curHealth = 0;
 
         // Cur HP cannot be higher than max HP
         if (curHealth > maxHealth)
             curHealth = maxHealth;
 
 
         healthBarLength = (Screen.width / 4) * (curHealth / (float)maxHealth); // Full health length bar * (% of current health)
         }
 
     void Update(){
         numShur = ShurikenProj.numShurikenProj;
         //UpdateHealth (0);
         }
 
 
 }