How do i control the cirle on C# forms?

Hellow everyone. I have problem on C# forms application. I want to make a dart game. The cursor is ok. It will be moving automaticly, when you're clik on form it will be shot the form. But I can't calculate the score. How can i find where shotted on form's background image scores? By the way the arrow is a label and i creating that thing when you cliking on form.Sorry for bad English and thank you ...