WeekSpeller

I am currently struggling with this issue where I am not able to estimate efforts properly for stories and they get moved out of the sprint because I could not finish them on time.

There are multiple reasons for that.

1. I work on a legacy codebase and our lead told us to refactor along with normal task. It means every story has some wider scope that it looks from the title and description.

2. I am a wanna be perfectionist and try to refactor the older code and make it "beautiful" even when I am not told to do it, so I end up with a wider scope than the story was initially planned

3. Sometimes when I am in the "zone" and I find the work interesting I do finish task very quickly but when I am not in the "zone" I struggle to even write basic unit tests. This has given me a false sense of "quickness" in my mind and I end up overcommitting. How do I overcome this?

I would like some advice from the experienced devs out there. Please help.

I am usually good at creating design and architecture for the problem at hand, but I really suck in documentation.

I get confused between different UML diagrams and how to put the architecture in different blocks and represent relationship between them? OR how much should this sequence diagram cover? Should it be covered in flow diagram or sequence diagram.

This is holding me back and I have no clue how to improve this. This has been brought up during the performance review.