Hermie:
Perhaps your instructor has reinvented flying? Pray tell me what he allows you to use the ailerons for?
More than one person on this thread has offered advice, have you taken it?
Can you find another instructor?
I remember a bad movie about 48 years ago and someone was talking down someone else who had not flown this type of plane before and they kept telling him to use the rudder for small adjustments. BUT IT WAS A MOVIE.
Hermie, our advice won't work if you don't take it.
Oh, one other thing. Does the slip skid ball stay centered while your instructor uses this rudder only technique? If it does, I would be surprised.