writeablebitmapex FillEllipseCentered with center out of boundary

Mar 31 at 8:06 AM
I have writeablebitmap with width and height equal to 580, i need to draw a circle in it. So i will use bmp.FillEllipseCentered(290,290,290,290,color);

I need to zoom this circle by scaling factor 2, say the radius will be 290 *2 = 580, so that i will move the scroll bar and i will be able to see the curves of the circle by changing the center position.

When i zooming again, circle is not coming i was getting some lines at the end region. Is there any way to achieve this zoom in this fillellipsecentered by scalingfactor.
bmp.FillEllipseCentered(1160-x,1160-y,1160,1160,color);.. i was not getting circle or curves