[Can I request a refund from the seller?]

Hello, can I ask for a refund from my seller?
So I ordered a 20 chapter story writing gig with a 40 day deadline.
But from 28Dec - 11Dec (2weeks) he has just finished 4 chapters....I want to stop using his services, and just pay for the chapters he's already done. I'm actually satisfied with his work, but I'm also pressed for time, because I have to publish 1 chapter/ 2 days
Will it affect his rating on fiveer?