Aspect Ratio for drawing circle

I’m trying to properly display a circle series as a circle. I’ve made sure the graph is not resizable, and set the GridLinesPanelStyle to ensure that it’s square. However, when do ZoomExtents on the ViewPortManager, it always adds a little buffer space on the Y axis but not the X so you end up with an ellipse. Is there any way to set and/or remove this buffer? You can see this in the image, the graph itself is square and the range on the X axis is 300, but on Y it’s a little bit bigger so what you see isn’t really a circle. Thank you.