Just now I tried to simulate your results. I got the same numbers pulling a stroke of length 80cm at 150N (15kg) handle force, rating 27 spm. Data shown in Ergdata. Not sure that this power (50W) can have any effect on fitness; but we all started somewhere and can only explore our possibilities.
Try longer and harder strokes, say 100cm length and 200N force, rate 23. This would equate to:
1 x 200 x 23 / 60 = 75W. You will need to engage your legs, pushing harder with a longer stroke, and will likely see higher HR.
For reference, if you climb a flight of stairs (3m height) in 20 seconds, with all up weight say 75kg, your power output, from legs alone, would be 3x75g/20 = 110W, which is roughly double your erg power, and all done by the legs.
This may be a key point for you: despite what we may think we see, rowing is a leg sport, since that's where the big muscle is, in hips and thighs; producing 80-90% of the total work done. The amount of work they can do, even though I usually stop well short of sudden death, always amazes me.
C2's founders were oarsmen and are very good at making us work hard. They know very well how we can best use their machines, and show it here:
https://www.concept2.com/indoor-rowers/ ... que-videos
08-1940, 179cm, 83kg.