What size circles are you doing?
I can't help with the puckering but in order to get your circles, well circular, think of them as squares. Think of your four points and connect each point using an arc. Look forwards towards your next point, not at where you are.
Hope that helps in the geometry department.
The toughest thing for me about ruler quilting is remembering to keep the foot against the ruler or template. If you can keep the foot snug against the ruler you've got it.
Watson.