How can I retract a transfer that hasn't settled yet?

The easiest thing is to simply complete another transfer, before the prior transfer settles.

This newer transfer will replace the prior transfer, invalidating it.

Because Zucoin uses two-way transaction confirmation, a transfer isn't final until both parties have confirmed it, giving you time to supersede an unwanted transfer with a new one.

More on this topic:

Do transfers still expire automatically?

How do transactions work?

What are the benefits of a 2-way transaction authentication?