Player cannot double jump

Hi, i am following a tutorial on youtube and everything is working fine until now, except i can only have one jump with this code, any advice ?

using UnityEngine;

using UnityEngine.UI;

using System.Collections;

public class Player : MonoBehaviour {

 public float power = 500;
 public int jumpHeight = 1000;
 public bool isFalling = false;

 public int Score;
 public Text SCORE;
 public GameObject YOUDIED;

 private int health = 3;
 public GameObject health1;
 public GameObject health2;
 public GameObject health3;

 public int Highscore;

 private bool canDoubleJump;
 private bool jumpOne;
 private bool jumpTwo;

 // Use this for initialization
 void Start () {
     YOUDIED.SetActive(false);
     Highscore = PlayerPrefs.GetInt ("Highscore", 0);
     jumpOne = false;
     jumpTwo = false;
     canDoubleJump = false;
 }
 void Update() {
     if(Input.GetMouseButtonDown(0) && health == 0) {
         Time.timeScale = 1f;
         health = 3;
         Application.LoadLevel(0);
     }
     if (health == 3) {
         health1.SetActive (true);
         health2.SetActive (true);
         health3.SetActive (true);
     }
     if (health == 2) {
         health1.SetActive (true);
         health2.SetActive (true);
         health3.SetActive (false);
     }
     if (health == 1) {
         health1.SetActive (true);
         health2.SetActive (false);
         health3.SetActive (false);
     }
     if (health == 0) {
         health1.SetActive (false);
         health2.SetActive (false);
         health3.SetActive (false);
     }
     if (health <= 0) {
         YOUDIED.SetActive (true);
         Time.timeScale = 0.0f;
     }
     SCORE.text = "Score " + Score;
     transform.Translate(Vector2.right * power * Time.deltaTime);
     if (Input.GetKeyDown(KeyCode.Space) && isFalling == false) {
         jumpOne = true;
         canDoubleJump = true;
         isFalling = true;
     }
     if (Input.GetKeyDown(KeyCode.Space) && isFalling == true && canDoubleJump == true) {
         jumpTwo = true;
         canDoubleJump = false;
     }
 }
 void FixedUpdate() {
     if (jumpOne == true) {
         GetComponent<Rigidbody2D>().AddForce(Vector2.up * jumpHeight);
         jumpOne = false;
     }
     if (jumpTwo == true) {
         GetComponent<Rigidbody2D>().AddForce(Vector2.up * jumpHeight);
         jumpTwo = false;
     }
 }
 void OnCollisionStay2D(Collision2D coll) {
     if (coll.gameObject.tag == "Ground") {
         isFalling = false;
         canDoubleJump = false;
     }
 }
 public void ScorePlus(int NewScore) {
     Score += NewScore;
     if(Score >= Highscore) {
         Highscore = Score;
         PlayerPrefs.SetInt ("Highscore", Highscore);
     }
 }
 void OnTriggerEnter2D(Collider2D coll) {
     if (coll.gameObject.tag == "Death") {
         health -= 1;
     }
 }

}