and used Grammarly to improve on it.

This here is the problem. You may only use Grammarly for light editing which includes spelling and punctuation corrections, and light grammar corrections eg: using the correct form of the verb. You may not use the advanced AI functionality of Grammarly to rephrase, improve, or create better fluency in your piece as this means that the end result contains writing significantly different from your own. You still need to use your own words. The more you read, the more you write, and the more feedback you take on board, the more you will see organic development and improvement in your writing :-) Kindly refrain from using these advanced features of Grammarly. You may find editing in Google Docs to be a better option for you if you still find this explanation unclear.