Check sideways bend. Repeat with genoa, if conditions aren t too extreme. The leeward shroud should be firm, not floppy at a 20 degree heel. Now adjust diagonals to straighten mast sideways. Sail Control Bend Mast bend is used for sail control.
All mainsails have luff curve which creates sail shape.
With the mast straight, the sail will have shape. If you bend the mast to exactly to fit the luff, the sail will be almost dead flat. In light to medium air, especially in a chop, use only a little bend and power up the main. In heavy air, bend the mast more and the sail will depower allowing the boat to stand up better and be easier to handle. A good rule of thumb is to limit mast bend deflection to amount equal to the fore and aft dimension of the mast.