When rewriting your opening, ask, “Why would the reader want to read on?” and, “Why did I start my novel with that line, or in that way?” The “right” opening to your novel is the crucial “hook” to keep your readers going. Likewise, the “right” ending is critical to bringing your readers back.
Although I love the idea that, “Art is never finished, only abandoned” (Leonardo da Vinci), as an author I nevertheless must decide when to type “The End.”
To be clear, when writing a non-fiction book, I pretty much know at the start where it will end. However, as a novelist, deciding when the book will end is more an agreement between me, the story, and one or more of the characters.