Problem setting Time.timeScale to 1 after being set to 0

So I've just made a script that will pause the game and bring up a window with three buttons (main menu, retry and continue) once the player has completed the level or failed it. This is what it looks like, except when the player fails (run out of time), it says "You ran out of time!". Apart from that there is no other difference. All the buttons function the same regardless.

When the player completes the level or fails it, Time.timeScale is set to 0. This is when the window comes up and the player can click on one of the buttons (what they do is self-explanatory). Now if the player completes the level and then chooses one of these options, Time.timeScale is set to 1 and will load the scene, and everything works perfectly. However, if the player runs out of time and fails, when the player chooses to go to the Main Menu, retry or continue, Time.timeScale doesn't seem to set back to 1 and the game is still paused but the correct scene is loaded so I know the function is being called. I know it's something to do with the timer as I've called the same Fail function I created using OnCollisionEnter (so when the player collided with a certain object they fail), and everything worked as it should. I'm not a programmer so maybe the answer is completely obvious but here is the script:

     private int levelNumber;
 
 
     public Canvas endLevelCanvas;
     public Text outcomeText;
 
 
     public Text timerText;
     public float startTime;
     private string currentTime;
     
     // Use this for initialization
     void Start () {
         levelNumber = Application.loadedLevel;
 
         endLevelCanvas.enabled = false;
         
     }
     
     // Update is called once per frame
     void Update () {
         
         startTime -= Time.deltaTime;
         currentTime = string.Format ("{0:0.0}", startTime);
         timerText.text = currentTime;
         if (startTime <= 5) {
             timerText.color = Color.red;
         }
         if (startTime <= 0) {
             FailLevel ();
         }
 
         if (Input.GetKey (KeyCode.Escape)) {
             QuitToMenu ();
         }
     }
 
     public void FailLevel () {
         Time.timeScale = 0;
         endLevelCanvas.enabled = true;
         outcomeText.text = "You ran out of time!";
     }
 
     public void WinLevel () {
         Time.timeScale = 0;
         endLevelCanvas.enabled = true;
         outcomeText.text = "Level Completed!";
     }
 
     public void QuitToMenu () {
         Application.LoadLevel (0);
         Time.timeScale = 1;
     }
 
     public void ContinueToNextLevel () {
         Time.timeScale = 1;
         Application.LoadLevel (levelNumber + 1);
     }
 
     public void RetryLevel () {
         Time.timeScale = 1;
         Application.LoadLevel (levelNumber);
     }
 }

Sorry if I've missed something, I'm new to Unity Answers. Any help is greatly appreciated, thanks!