EGKB,
You might feel its nit picking, many of us on here come from a background where the devil is in the detail. It may be in written format or through certain actions. Make a mistake and it can have serious consequences. The one thing that is common to all the people that have offered you advice is that they are further along the learning curve than you. They have also learnt to listen and absorb / apply what they are being told.
You talk of being able to fly +/- 20' of selected altitude, what about the other varibles? What happened with the heading, what was your airspeed? was that constant? where was the ball with respect to balance, was it a turbulent day? and was the accuracy maintained for a decent time (say 20 minutes).
At the moment your written responses show poor attitude, perhaps thats not what you want - if that's the case, then don't be in such a hurry to respond, consider your response and then act.