restrict number of double jumps

Hi, i am trying to set a limit of doubles jumps available to the player. so for this code i am using i have set the limit to 5 and every time the player double jumps it is reduced by one. so that when it reaches zero then cannot use double jump anymore. however it seems to have back fired and allows the player to continuously jump in the air, even when not on the ground. please help. using UnityEngine; using System.Collections;

public class CharacterMove : MonoBehaviour {

 public float speed = 6.0f;
 Transform groundCheck;
 private float overlapRadius = 0.2f;
 public LayerMask whatIsGround;
 private bool grounded = false;
 private bool jump = false;
 public float jumpForce = 700f;
 private bool doubleJump = false;
 public int dJumpLimit = 5;


 void Awake()
 {
     rigidbody2D.fixedAngle = true;
 }

 void Start()
 {
     groundCheck = transform.Find ("groundcheck");
     PlayerPrefs.SetInt ("doublejumps", dJumpLimit);
 }

 void Update()
 {
     //if (Input.GetKeyDown (KeyCode.Space)){
     //                jump = true;
     //}    
     if (Input.GetMouseButtonDown (0)) 
     {
         jump = true;
     }
 }

 void FixedUpdate()
 {
     //check if character is grounded
     grounded = Physics2D.OverlapCircle (groundCheck.position, overlapRadius, whatIsGround);

     //reset doublejump when player is on the ground
     if (grounded)
         doubleJump = false;

     //determine if player can jump
     bool canJump = (grounded || !doubleJump);

     if (jump && canJump) 
     {
         rigidbody2D.velocity = new Vector2(rigidbody2D.velocity.x,0);
         rigidbody2D.AddForce(new Vector2(0, jumpForce));
         if(!grounded && dJumpLimit >= 1)
         {
             doubleJump = true;
             dJumpLimit--;
         }
         else if(!grounded && dJumpLimit <= 0)
         {
             doubleJump = false;
         }
     }

     jump = false;

     //apply forward movement
     rigidbody2D.velocity = new Vector2 (speed, rigidbody2D.velocity.y);

 }

}