Tic-Tac-Toe Simulator

So I am writing a tic tac toe simulator. One where it is only the computer playing, there is no human player. I have the program written but I am having some issues with an error and some graphical things.
1. I'm receiving and error on the return null; statement it says it is an invalid token. 2. My output on the form is made of labels but my labels are not in a grid layout and with very small text, I can't figure out how to make them bigger. 3. I want to add lines on the form like you would see when someone hand draws the game, however I am unsure how to get those drawn on the windows form. It seemed that I was also not consistently declaring a winner with the message box, and it seems that I've never see X win...it could just be a coincidence. Any and all help is appreciated. Thanks in Advance!

namespace kjblkblt
{
public partial class TTT_frm : Form
{
    private Random Generated = new Random();
    private Point LastMove;
    private const int Board_Size = 3;
    const int Squares = 9;
    char[] XorO = new char[Squares];

    public TTT_frm()
    {
        InitializeComponent();
    }

    private void TTT_frm_Load(object sender, EventArgs e)
    {

    }

    private void Sim_btn_Click(object sender, EventArgs e)
    {
        //Erase contents of Array
        for (int i = 0; i < Squares; i++)
        {
            XorO[i] = ' ';
        }
        //Erase contents of Results label
        Result_lbl.Text = " ";

        //Set fist and second player X's and O's
        char FirstPlayer = 'O';
        char SecondPlayer = 'X';

        //Generate the random numbers for the grid
        int[] position = new int[5];
        position[0] = Generated.Next(9);
        for (int i = 1; i < 5; i++)
        {
            int temp = Generated.Next(9);
            for (int j = 0; j < i; j++)
            {
                if (temp == position[j])
                {
                    i--;
                    break;
                }
                else
                {
                    position[i] = temp;
                }
            }
        }

        //Get first players positions
        for (int i = 0; i < 5; i++)
        {
            XorO[position[i]] = FirstPlayer;
        }

        for (int i = 0; i < Squares; i++)
        {
            if (XorO[i] != FirstPlayer)
            {
                XorO[i] = SecondPlayer;
            }
        }

        //Put the X's or O's in the labels
        A1_lbl.Text = XorO[0].ToString();
        A2_lbl.Text = XorO[1].ToString();
        A3_lbl.Text = XorO[2].ToString();
        B1_lbl.Text = XorO[3].ToString();
        B2_lbl.Text = XorO[4].ToString();
        B3_lbl.Text = XorO[5].ToString();
        C1_lbl.Text = XorO[6].ToString();
        C2_lbl.Text = XorO[7].ToString();
        C3_lbl.Text = XorO[8].ToString();

        //See Who Won
        switch(Winner())
        {
            case 'O':
                Result_lbl.Text = "O Wins!";
                break;
            case 'x':
                Result_lbl.Text = "x Wins!";
                break;
            case 'T':
                Result_lbl.Text = "It Was a Tie!";
                break;
         }            
    }

    private void GenerateNextStep(char playerChar, char[][] gameBoard)
    {
        int x;
        int y;

        if (LastMove ==null)
        {
            //Is the first move and can place anywhere
            x = Generate.Next() % Board_Size;
            y = Generate.Next() % Board_Size;
        }
        else
        {
            Point p = FindClosest();
            x = p.x;
            y = p.y;
        }
        gameBoard[x][y] = playerChar;
        LastMove = new Point(x, y);
    }

    private Point FindClosest()
    {
        for (int x = LastMove.x - 1; x < x +1; x++)
        {
            if (x < 0 || x >= Board_Size)
            {
                continue;
            }
            if (gameBoard[x][y] == ' ')
            {
                return new Point(x, y);
            }
        }
    }
    return null;

    private char Winner()
    {
        //Return result of game so that a determination can be made
        //Returns X, O or T
        char winner = ' ';
        int Win_Sequence = 0;

        //Columns
        if (XorO[0].Equals(XorO[3]) && XorO[0].Equals(XorO[6]))
        {
            Win_Sequence++;
            winner = XorO[0];
        }
        if (XorO[1].Equals(XorO[4]) && XorO[1].Equals(XorO[7]))
        {
            Win_Sequence++;
            winner = XorO[1];
        }
        if (XorO[2].Equals(XorO[5]) && XorO[2].Equals(XorO[8]))
        {
            Win_Sequence++;
            winner = XorO[2];
        }

        //Rows
        if (XorO[0].Equals(XorO[1]) && XorO[0].Equals(XorO[2]))
        {
            Win_Sequence++;
            winner = XorO[0];
        }
        if (XorO[3].Equals(XorO[4]) && XorO[3].Equals(XorO[5]))
        {
            Win_Sequence++;
            winner = XorO[3];
        }
        if (XorO[6].Equals(XorO[7]) && XorO[6].Equals(XorO[8]))
        {
            Win_Sequence++;
            winner = XorO[6];
        }

        //Diagonal
        if (XorO[0].Equals(XorO[4]) && XorO[0].Equals(XorO[8]))
        {
            Win_Sequence++;
            winner = XorO[0];
        }
        if (XorO[2].Equals(XorO[4]) && XorO[2].Equals(XorO[8]))
        {
            Win_Sequence++;
            winner = XorO[2];
        }

        if (Win_Sequence == 0 || Win_Sequence > 1)
        {
            winner = 'T';
        }

        return winner;
    }

    private void Exit_btn_Click(object sender, EventArgs e)
    {
        this.Close();
    }
}

}