The simplest circle jig I've ever seen is one made by past member Derek Willis. It's just a piece of shop scrap wide enough for the router to sit stably on that has been drilled with a hole the same size as the O.D. of a guide bushing. You then install the guide bushing on your router and stick it in the hole and then drive a nail through your jig and into the center of where you want the circle.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.