How to handle constant feedback from your scrum master in your team that you need to improve, and that you have not still reached that stage?
Generally speaking, you have to deal with it. Because SCRUM is about constantly improving and the SCRUM masters job is to tell you how you can improve in the process of SCRUM. So theoretically, everything is as it should be.
Some things you said make me think that maybe SCRUM is not fully understood by all members of your organisation. Although the SCRUM master should be free to point out small things immediately (like "you are late we agreed on 10:30" or "please update the cards on the board at the time we specified"), general feedback should be left for the Retrospective, because you need to focus on your work in the sprint.
Feedback concerning the quality or quantity of your work should never come from your SCRUM master. That should come from your team mates, maybe in the same retrospective. Because your SCRUM master is not responsible for the product's quality, it's the team. The SCRUM master might not even be able to judge it. That's not his or her job.
So the bottom line is, you will need to continually improve. Both concerning processes as well as in the quality of your own work. Both should not come as constant nagging, but just as you are focused on your work in a sprint, feedback should be focused in the retrospective meeting after each sprint.