Going off course is realistic, depending on your settings.  Turbulence can cause roll, as well as some effects of your sim.

Which is why that in my quest to do a RTW in a single engine prop, i desperately want to find one with an aileron trim tab...  between it being unbalanced becase of fuel and torque, having to constantly have my hands on the stick to keep the VOR centered is quite annoying.

Thanks, Nav.  The tweak to the Vimy made it perfectly flyable.  A short hop across England at 4000ft found her quite stable, not only was I not hauling back on the stick continually, I was able to go for a snack without her drifting too far off course.