What is an antonym of improved/improvement?
Solution 1:
I think I like regress(ed|ion) or deteriorat(ed|ion).
Comparing the words to "worsen" [which I believe is barely English].
Usage:
My essay quality deteriorated as I made each edit.
How did your essay regress after making changes?
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regress: return to a former or less developed state.
deteriorate: become progressively worse.
Solution 2:
"I degraded [the {quality / standard} of] my essay".