Question

Is it okay if the prologue of my book is actually set after the book ends?

Answer 1

Yes

Explanation:

A prologue is an introduction to the main body of the book.

There is no need for a prologue to describe things chronologically before the main body of the text.

For example, if you were writing a biography of someone else, you might well start with a summary of how the person described is seen now, and remark that they started from a very different and unexpected place.