When I had to sew bunches and bunches of circles what I did was used a thumb tack I took a couple layers of tape stuck the thumb tack through the tape I then found the EXACT center of the circle I was trying to sew put the thumb tack though that spot (take on the under side with the sticky side down. But the needle in the fabric right on the line I had to sew then pushed the tape down in the right spot so it would hold the fabric at the exact spot and I just have to quide it around!
Thats about as clear as mud isn't it? If this kid of mine would ever go to sleep I would set my machine up and take a picture of what I did! lol