The mechanics of a circle are:
Inside leg at the girth, keeps the circle from falling in
Outside leg slightly back, keeps the high end from falling out
Outside hand holds, keeps the size of the circle
Inside hand bends, directs the circle
Obviously these aids do more then what I just listed but they're the basic aids for the circle. Once you get those down you have to get a 'feel' of how much of each aid you need. There is no "formula" of which aid you use the most, it will depend on your horse and situation. If your horse is falling into the circle, do you need more inside rein? Probably not. The inside leg and outside rein (as others have mentioned) will keep the circle big. So you might be using those aids but you might not be using them enough or at the right moment. Or your horse may not be responsive to them. That's a whole other question... As Spyder mentioned in another post, if your mom is a stellar dressage rider she should be able to help you with something like this.