I think what might help, and take this with some leniency , as I dont' really show , is to think of having the horse really almost pushing toward the outside ring of your circle. When you have him bent on the circle, there should almost be a feel of tension along the outside aids, outside rein and outside leg. a feel of the horse filling up the outer edge . Sally Swift talks about it as the way water would gush through a turning chute at a water park; it would push against the restraining wall on the outside of the curve.
Once you set the bend to follow the circle, if the horse is correctly connected with it's energy to the outside rein, you almost have to do nothing because if the arc is correct, just follow that arc and it will make a perfect circle.