I agree with Chris.
First check the halyard
tension - no horizontal creases in the luff or crow's feet at the slides.
Then set up the angle of attack with the traveller if you're close enough to the wind
Then pull the boom down with the sheet to reduce the twist.
If further off the wind
the traveller is less useful (it needs to be down to leeward) and you control the angle of attack with the sheet; crank on the kicker
to reduce twist.
Not the leech line though - that just controls the extreme edge of the sail.
Or maybe the sail's horribly stretched :-(
(Hope I'm not talking out of my sternport)