Freelancer.com, how to change the price (after I was accepted as an executor) or not ruin the rating?

Question

Freelance

Let me know who has come across.
Left a comment on the project, on freelancer.com. I was chosen as a performer.
Everything was done quickly and efficiently. The customer is satisfied.
But as it came to closing the project's board, it turned out to be a jamb. The customer in the text indicated that the price for the work is fixed, for example $20, and I indicated $25.
It turned out that both he and I were not attentive .. He refuses to pay me $25 due to the fact that the text indicates that the bet is $20, no more - no less, but I indicated $25 and he accordingly chose me as a performer, not seeing that I set the price at $25.
Now the price can no longer be changed.
How to get out of the situation? so it doesn't show up in the rankings?
(I already have one positive answer there and registering a new acc is not an option)

Answer 1

Be more careful next time. Learn from your mistakes :) 25 - 20 = 5. That's how much your new experience is worth. I think it's not that much.

Answer 2

Agree on 20 - definitely will not affect the rating.

Answer 3

for five bucks, there’s no point in simmering, if you can’t officially change the price, he got 5 dollars himself, but explain to him that it’s his fault, and at least let him write a nice review