If your having a lot of issues getting it to roll axially, install another, larger set of stab fences along with what you already have. That will lock the tail in better and help with the rolls. Also, accurately measure the throws of the ailerons with something that can get you measurements within about .1 degree. I use pointers and a homemade protractor. But each aileron must be throwing the same. Then you can dial in the differential with the radio system.
Another way of checking if you have sufficient yaw stability is the spin entry. If it tends to drop a wing before you're ready to enter, then you need the larger stab fences.