Draw fractal Fit inside panel using Winform?

[gopal0430]

Hi I am trying to build a windows application in .net which draw fractal image inside the panel.It take end points of line as starting point of next line.But problem is, diagram is going outside of the panel.How do i fix drawing inside the panel

 static int start_x, start_Y;
        static int end_x, end_Y;
        static int my_angle = 0;
        static int my_length = 0;
 
 public void draw_line()
        {
 
             Pen mypen = new Pen(Color.Orange, 2F);
                my_angle = my_angle + (74);
                my_length = 100 + (1);
 
                end_x = (int)(start_x + Math.Cos(my_angle * .0174539676) * my_length);
 
                end_Y = (int)(start_Y + Math.Sin(my_angle * .0174539676) * my_length);
                Point[] points =
            {
                new Point (start_x,start_Y),
                new Point (end_x,end_Y)
            };
                start_x = end_x;
                start_Y = end_Y;
 
 
            Graphics g = panel1.CreateGraphics();
             g.DrawLines(mypen, points);
 
        }
 private void panel1_Paint(object sender, PaintEventArgs e)
        {
            start_x = panel1.Width / 2;
            start_Y = panel1.Height / 2;
            for (int i = 0; i < 400; i++)
                draw_line();
        }