Re: Pulls hard left.
What works for me is to trim motor until pressure on the steering wheel lets off. Much beyond that, the prop starts to ventilate.
However, your 20 hp Merc may just be a fixed trim that you adjust amont 4 or 5 holed on the motor mount like my old 40 hp merc, 1980 vitage did. Experiment raising it up from first hole to next until steering feels right. If she still pulls, keep asking for alternate solutions.