Don't worry, you are most definitely not alone! Marking helps, even if you just mark registration lines. Some people use their hopping foot as a gauge for the spacing of the spiral within each circle. The only quilter I know of who seems to make perfect spirals every time is Diane Gaudynski. Hers are just beautiful. She emphasizes to envision the shape before you quilt. I have not had much luck with that so I just do the best I can. Many times, if you see perfectly spaced and proportioned spirals in quilting it is either computer guided or template guided.