You will need to simplify the ellipse layer then find the Stroke command. On my version, #4 I think, it's on the Edit menu. There you will be able to select the size, # of pixels, and color of your line. For a double line effect:
1. Stroke with any color other than your background color.
2. Making sure the Outside (not Center or Inside) option is checked stroke again using the background color.
3. Stroke a third time with either the same color as the first line or a different one making sure that Outside is still checked.