如何在WPF中调整多边形的大小？

I'm working on my first WPF application and I'm testing out a custom control that is essential a circle with a play button drawn into the middle of it. I seem to have hit a bit of a hitch though. When I draw my play button I can't seem to get it to resize alongside the circle. Specifically, when I resize the circle to be wider or taller, the play button polygon remains the same size and in the same absolute position. Any pointer on setting up my XAML or code to correct this?I'm working on my first WPF application and I'm