I feel you would be far better served by separating the creation / conversion into two distinct operations.
First, completing your masterpiece in Word, but ONLY the actual text of the book itself.
Then, convert what you have into an ePub format. (Hopefully breaking the story into multiple files at chapter breaks).
Finally, using a tool more designed for handling ePubs add in the entities like cover page / title page / dedication / copyright etc.
You would also gain from the experience of other, more skilled ePub creators by moving to the dedicated
ePub format sub-forum, and of other authors in the
Writer's Corner sub-forum.