Buyer cancelled the order and ruined my 100% positive rating.

Buyer cancelled the order saying that i was not able to deliver the order on time, the fact that he never replied to my messages he didn't provide me any instructions to work on, I have contacted the buyer and now he want to correct this. I had 100% positive ratings before this incident and now the ratings has been ruined for no reason. Please tell me how this can be corrected. :(

Thanks!