The foundation of any efficient movement is to have good mobility. If you want to possibly go beyond what you can identify on your own you may want an evaluation with a Sports Scientist/Therapist. They can customize a set of dryland drills to improve your overall mobility as well as the balance between your dominant and non-dominant sides.
Dumbbell drills for your non-domiant side can help you catch up and achieve whole body balance (Hayley Nixon Find and Correct Imbalances).
Tight hamstrings are prevalent among athletes. Two minutes in the morning and evening can yield loser hamstrings and better posture in the boat. You may find pulling on a band wrapped around your heels helpful in increasing your stretch.
These stretches help improve the range of motion during rotation in the stroke.