var panel = sender as TableLayoutPanel;
e.Graphics.SmoothingMode = SmoothingMode.HighQuality;
var rectangle = e.CellBounds;
using (var pen = new Pen(Color.Black, 1))
{
    pen.Alignment = System.Drawing.Drawing2D.PenAlignment.Center;
    pen.DashStyle = System.Drawing.Drawing2D.DashStyle.Solid;
    
    if (e.Row == (panel.RowCount - 1))
    {
        rectangle.Height -= 1;
    }

    if (e.Column == (panel.ColumnCount - 1))
    {
        rectangle.Width -= 1;
    }

    e.Graphics.DrawRectangle(pen, rectangle);
}