What rowing machine did you go with? regardless, there are apps and guides out there to help with form. Personally, I'd say just take it easy and enjoy some media while you get base kilometers in for a time. one thing, feet being narrow together can be an issue for the testicles if you got them, so don't be afraid to widen the foot pad a touch to make sure it works for your body. don't let those elbows flare out too much and focus on form. after a few weeks of that just give her and it's painless fun (except for the lungs).

As an aside, because it warms your whole body pretty well, stretch afterward. I find it helps. I blew out my knee playing rugby and a rower was my choice activity after I got of crutches. I went from potato back to how I was.

Hope that helps!