Simple Coding Error Help - C# - Following Packt Book

Got this error following a simple tutorial in the packt book - Unity Android Game Development By Example.

Its a simple game of TicTacToe it seems my boardIndex is not right...

I can't work it out - any help would be greatly appreciated.

Error Code: IndexOutOfRangeException: Array index is out of range. TicTacToeControl.OnGUI () (at Assets/TicTacToeControl.cs:18)

Script:

 using UnityEngine;
 using System.Collections;
 
 public class TicTacToeControl : MonoBehaviour {
 
 public SquareState[] board = new SquareState[9];
 public bool xTurn = true;
 
 public void OnGUI() {
     float width = 75;
     float height = 75;
     
     for(int y=0;y<3;y++) {
         for(int x=0;x<3;y++) {
         
         int boardIndex = (y * 3) + x;
     Rect square = new Rect(x * width, y * height, width, height);
     string owner = board[boardIndex] == SquareState.XControl ? "X" : board[boardIndex] == SquareState.OControl ? "O" : "";
     
     if(GUI.Button(square, owner))
         SetControl(boardIndex);
         }
     }
 }
 public void SetControl(int boardIndex) {
     if(boardIndex < 0 || boardIndex >= board.Length) return;
     
     board[boardIndex] = xTurn ? SquareState.XControl : SquareState.OControl;
     xTurn = !xTurn;
     }
 }