Hi. As far as I know, the automatic 1* cancellation only happens when a seller doesn’t deliver at all and lets the order go into Very Late status and the buyer chooses to cancel.
(This, I know from experience - as the buyer, luckily; if a seller will let the order go “very late” and won’t respond to messages at all, and you finally cancel to get your money back, you, as the buyer, have no choice in this, that 1* review with Fiverr’s default text will happen automatically. Had I not canceled finally, the undelivered order would just have lingered in my dashboard forever, apparently.)
In your case, this should happen:
Mutual Cancellations: This is one way to resolve an order that both parties can’t agree on. If one side requests and the other accepts within 24 hours, then the order is cancelled mutually. If a buyer doesn’t respond within two days of a seller initiating a Mutual Cancellation, the Gig is automatically canceled and the cancellation is listed as seller > initiated.
Customer Support: If sellers and buyers don’t agree to a mutual cancellation, then contacting Fiverr Customer Support is the next step.
The cancellation will affect your order completion rate but that should be it (of course, you need your completion rate to stay at min 90% to not lose a level on next evaluation date, so, good luck with that).
Whether you should have canceled when you delivered what was agreed or your gig promised, is another question, but your decision, of course, I can imagine that one modification request after the other without any comment gets very annoying.