There are different ways to do it... I have been experimenting with different methods I have read/seen, etc
You can cut out a cardboard circle the size of your finished circle..cut fabric...sew a basting stitch all around edge of fabric, put, cardboard, or template in fabric, pull the basting and as you hold it tight press it down...take out cardboard and secure your basting stich...no need to take it out...i only do this for small ones..I find this takes too long but works well...
I have also used freezer paper, starch the edge with a brush and pressed seam allowance to back...take out freezer paper before i sew down..use a Clover craft iron and it is easier...
..now i try just to needleturn as i go...trick is a small seam allowance..1/8 inch if possible..when i first started this seam allowance was too small, as I have improved, it becomes easier to manage the small seams...