Issue with limiting the rotation of an object on Z-Axis

Hi

I'm pretty new to unity and i use it in a special way of creating a non-game2D application So i work only with UI element. I'm having some issues with something i want to do . I have an object which rotate following the finger (or mouse) but the object must not get out of the "area" Here is my code for now :

 using UnityEngine;
 using System.Collections;
 
 public class SteeringWheel : MonoBehaviour
 {
     public float angleMax = 90.0f;
     private float baseAngle = 0.0f;
 
     void OnMouseDown()
     {
         Vector3 pos = Camera.main.WorldToScreenPoint(transform.position);
         pos = Input.mousePosition - pos;
         baseAngle = Mathf.Atan2(pos.y, pos.x) * Mathf.Rad2Deg;
         baseAngle -= Mathf.Atan2(transform.right.y, transform.right.x) * Mathf.Rad2Deg;
     }
 
     void OnMouseDrag()
     {
         Vector3 pos = Camera.main.WorldToScreenPoint(transform.position);
         pos = Input.mousePosition - pos;
         float ang = Mathf.Atan2(pos.y, pos.x) * Mathf.Rad2Deg - baseAngle;
         Debug.Log("ang1 : " + ang);
         ang = Mathf.Clamp(ang, -90, 90);
         if (transform.eulerAngles.z >= 89 && transform.eulerAngles.z <= 271)
         {
             transform.rotation = new Quaternion(transform.rotation.x, transform.rotation.y, 0.7f, transform.rotation.w);
             return;
         }       
         transform.rotation = Quaternion.AngleAxis(ang, Vector3.forward);        
     }
 }

And here is a gif of the problem : http://img15.hostingpics.net/pics/324271Animation.gif