I stitch all my pieces by machine but have many decorative stitches on it. If I'm in a hurry Iuse the blanket stitch even on the circles and small piecies. I adjust the width and length depending on how small the piece is.
First do you have a knob or button to release pressure on your foot...This willmake it easier for you to turn around the circle without constantly lifting your foot. If you only have a zig zag stitch make it tiny...and you'll be fine. You should also use light tear away stablizer on the back of the fabric to avoid puckers