ContextMenuStrip showing on a left click

[Holly_vi]

I want my button’s ContextMenuStrip to show when the user clicks on the left mouse button, and not on the right one.
So, in the MouseDown event of the button I do the following:

if (e.Button == MouseButtons.Right)
{
    this.btn.ContextMenuStrip = null;
}
else if (e.Button == MouseButtons.Left)
{
    this.btn.ContextMenuStrip = this.btnConMenuStrip;
    this.btn.ContextMenuStrip.Show(this, PointToScreen(new Point(e.X, e.Y)));
}

The problem is that the ContextMenuStrip is not located where it’s supposed to be.
Am I doing something wrong?
Is there a better a way to achieve what I want?