If you're running your scanners at your desired rate, I would increase the size (in software if you have the size not at 100%) or gain on the drivers. The important thing is to get the circle close to the size of the square. If you change the gain you need to be careful to do this slowly and adjust the LF and HF damping to compensate as required.
It can sometimes be better, especially if you've not tuned scanners before, to follow Adam's (Buffo) excellent scanner tunning guide. This way you should end up with the scanners optimised for the size and rate you want to use.
Always tune slowly and carefully in case you unbalance them. At the first sign of instability, turn the adjustment back and move to another of the adjustments to compensate.