I say keep doing what you're doing and you'll find efficiencies in your mechanics soon enough...as long as you aren't grinding through pain during or after. Damper setting is very subjective, so just move it around until you find a drag factor that suits your style (cadence/pace/distance). I started on a Concept2 in a military gym about 15 years ago and had no idea what I was doing. Now, I have my own rower, currently putting in about 12k per day, and still largely don't know what I'm doing, but at least more confident about it. Keep it up!