Render output to 512x512. I used the Draw circle. And. Held shift. Then, stuck that in the lower right. Remembering the material basics lesson. Set the X array at 1m still works fine. Then, duplicate and change to Z. Everything else was the same I think. The guide was helpful like an invisble plane wherever you wanted that you could snap too.
While Grease Pencil doesn't (currently) have the guides (It's my understanding that they will, at some point, be added back in), you can still draw a circle using the Draw Circle tool. If you click on the symbol under the eraser that says "Box" when you hover over it and hold it for a second, you can pull up the option to switch to the circle. Then click and drag, holding the shift key to constrain to the circle instead of an ellipse, to create the circle guides. Press Enter to confirm the creation of the circle. To center the circle to the origin of the grease pencil object, you can go to edit mode and select the circle. If you don't have the right options panel already open, you can press N to pull it up and make sure you're on the Item tab. Under Transform -> Median: in that box, set the X, Y, and Z locations to 0 in Local mode. Now the circle should be centered on the origin of the grease pencil object. If the circle doesn't already have a fill, you can go to Stroke -> Set Stroke Type, and choose either FILL (for just a fill) or BOTH (to have both a stroke and a fill).
I tried to make this as detailed as I could, so I hope it helps!