You can also sew a circle in the middle. X's and O's :D:D:D
These circles go quicker than the X's. Meaure the width of your circle. get some tape and a thumbtack. poke the thumbtack up from the sticky side and securely tape it to the bed of your machine, half the width of the circle away from your needle. Finger press to find the center of your square and poke the center onto the thumbtack. Start sewing and you will sew a circle. Don't pull or tug at the fabric, or your circle will be distorted.