Everybody spins out some time or other.. Suspect its normally overoading fin before sufficient speed has been reached; a larger fin will provide more lift at lower speeds and could appear to alleviate the problem but the larger fin will bring other related problems (too much lift higher speeds/tail walk/less control are all possibilities)
Try a larger fin but I think wearing a GPS really helps;it may well help but you might well be travelling slower. Smaller/correct size fins (for allround play) do require a bit of technique to get best. Bare away initially until good speed has been attained and then head up to required angle; only loading fin up at speed) This is best way tget V max but possibly not best Vmg.. (Big fins are king of VMG)
PS Fins DO NOT CAVITATE. They airate..Completely different process.. Cavitation requires such low pressures that water boils/evaporates at certain spots.This produces pitting on stainless steel race props. (and submarine props) I`ve yet to witness any WS fins with cavitation damage ..Ws fins suck air down from surface and which produces loss of force;hence spin out..
Experiment but be objective. Find a fin that feels good but check its not inhibiting you in other areas.
Its all a compromise.