Try moving harness lines back ! (Lets rig go a little bit further forward;moves centre of effort of sail in front of centre of resistance of board.
With modern rigs its surprising how far back you can bring them.
(Rough guide. for a 5 metre front attachment point 5 fists from boom head; for a 6 metre 6 fists etc. OR harness lines at one third boom length back . Both only starting points. But check. Reckon its biggest cause of spinout.(Used to be crappy fins)
Also after landing sail down wind ; build up speed before loading fin up.Try and load up front foot; push board off wind.