You can sew a perfect circle using an old fashion thumb tack & a cork.
Tape tack to the left of your needle, point up, with good tape (think duct tape vs masking tape)
Put the center of your circle fabric over the tack and gently push down (cut larger than needed)
Smooth fabric under presser foot and lower foot
For your safety hold cork on point of tack
Slowly & evenly start sewing. Let the machine do the work.
Don't let yourself be distracted.
The feed dogs will pull the fabric around the tack.
Sew past where you started to lock the stitches.
Circle should be small & lightweight enough to 'float' on surface. If too heavy drag distorts circle.