I do the same thing that others suggested. Takes a little longer, but makes a perfect circle, no points around the edge. I sometimes make a pattern out of freezer paper doubled and iron the pattern to the back of the fabric. It can be used several times so if I need a lot of circles I make several. I do run a basting thread to gather the edge--gives me something to do while watching TV in the evening (if I don't keep my hands busy, I usually fall asleep).
Sue