Button Location Problems

At unity I've imported some textures as buttons, and placed them at their right place. To make them work I have used a logic that I was going to define some space limits in X and Y axis, and if the position of the mouse was at these limits(that would be set to be at the same size and place of the buttons image) when I clicked at the screen, the script would send a message to the debug telling the button I've clicked and change the scene, for a better notion, here is a class of a scene where the only thing the scene has is a button, and this script is the one i've used for it's configurations:

 //-------------------GAMEOVER.CS-------------------------------
 
 using UnityEngine;
 using System.Collections;
 
 public class GameOver : MonoBehaviour 
 {
     private float mousePosX;
     private float mousePosY;
 
     void Start () 
     {
         mousePosX = 0;
         mousePosY = 0;
     }
 
     void Update () 
     {
         if (Input.GetMouseButton(0))
         {
             mousePosX = Input.mousePosition.x;
             mousePosY = Input.mousePosition.y;
 
             Debug.Log ("X: " + mousePosX);
             Debug.Log ("Y: " + mousePosY);
 
             //-----------------------------------------
 
             if (mousePosX >= 258 && mousePosX <= 334 && 
                 mousePosY >= 4 && mousePosY <= 26)
             {
                 Debug.Log ("Main Menu");
                 Application.LoadLevel("Intro");
             }
 
             if (mousePosX >= 242 && mousePosX <= 348 &&
                 mousePosY >= 34 && mousePosY <= 71)
             {
                 Debug.Log ("Try Again");
                 Application.LoadLevel("Stage1");
             }
         }
     }
 }
 

The problem is: I used the li'l game window to click at the points of the buttons on the screen, see the cordinates debug shows me, and define the exact limits of the button to click, I compile the game and I click at the buttons at the game window, everything is just like the expected, but when I maximize the window to play, all of the clicking areas are terribly out of the place I've defined to be... Please Help Me to solve it

NOTE: The Game Canvas Size is 16:10.