It's difficult, but not impossible!

The challenge with balancing your harness lines is that it also depends on other things .. one day it will be perfect on your 6.0 next day .. bogus .. some of the really good guys downhaul their sails
exactly the same every time they rig, and then trim only using outhaul .. but not everybody has the luxury of 10 sales!
Assuming you've got your sail trimmed, mastrack ok, & footstraps comfy:
If you feel it is pulling on your back hand, move them back
If you feel it is pulling on your front hand, move them forward
..only small amounts .. cm's at a time make a difference. Lots of jumping on/off to tune them, until you learn what differences the changes make.
If your sail is wobbling, maybe you've outhauled too much making the sail too flat and the draught moves forwards/backwards..?
..crikey .. I think I'm just confusing you even more here! :-)
Hope you can make some sense out of the above... always a good idea to get someone better than yourself to watch you sail...it's always easier to see the mistakes in others, while missing them in ourselves...
Enjoy .. Lozza
p.s. Try taking the back hand off first, and see if you can sheet in/out just using body weight first...