Your swashplate should be LEVEL, although most single rotor heli's tend to list to the right during flight. I would check the servo linkages, are they equal in length, is there excessive play between the servo horn & swashplate linkages? Also check the servos, do they have stripped gears? Left & right balance could throw the heli off severely as well, (with your lower blades running fore/aft, lift heli up holding blade tips at mid-chord, does it list left/right?)
Just a few ideas for you to ponder.

Shadow