Good on you Colin for recognising your problem and asking fot help.
The fact that you sinker is landing right could be due to overloading the rod. Dont try so hard. Let the rod do the work. Body position will also effect you delivery. Try standing like you were about to play a tennis shot. Slightly side on. End the cast with the rod pointing skyward in the direction you want the sinker to go.
Theres about 100 other things to consider too. Try searching you tube forhelp with the "off the ground cast".
Good luck. It possible and just takes time. Took me two years to get the OTG cast sorted.