Writers: How to tell when you've finished your book?

I know there is a feeling. You get that feeling of complete happiness and satisfaction in that last line. I've gotten it many times in stories I have finished. The novel I'm writing now hot 80k words. I left it alone for just about a month. When I went back to it, my last chapter...It feels like I can... show more I know there is a feeling. You get that feeling of complete happiness and satisfaction in that last line. I've gotten it many times in stories I have finished.

The novel I'm writing now hot 80k words. I left it alone for just about a month.
When I went back to it, my last chapter...It feels like I can just call it The End for now. Edit it. Find my agent. Start with the next book that will be a continuation.
Problem...
I wrote a prologue down the road. Fell in love with it. But the prologue hasn't hit yet. I'd have to drop it . I'd use the scene in the next book; it's just I really loved it as a prologue.
Things would change...my outline would alter. Not in a bad way per se. It may actually help speed up the timeline instead of it dragging.

IDK. If I were to stop here...I got that feeling when I wrote that last line. I keep changing it a little bit. I tend to do that when I'm dealing with final lines in my stories. It's like a symptom. lol

I just feel so confused and typing this out does help me think a little bit more clearly.
Maybe I'm scared that I can say the book is done and now have to go on to editing and publishing.
Maybe I'm scared that I know I can finish a book in a year..b/c I didn't think that was possible for me.

So if you've read all of this...thanks for that.
And ane advice? Ane tips? Ane similar stories? Anething that may help?

Thanks in advance
and
Merry Christmas
Update: lol. has 80k words. not hot 80k words.
Update 2: Thanks so much for the answers! I'm always fine with changing my future outline. I do it all the time. I was just saying it'd shift it even more since I was stopping at a different point. But I'm totally fine with change. What else... The plot is very big. I can go on forever. It's not done.... show more Thanks so much for the answers!
I'm always fine with changing my future outline. I do it all the time. I was just saying it'd shift it even more since I was stopping at a different point. But I'm totally fine with change.
What else...
The plot is very big. I can go on forever. It's not done. That's why I need to make another book. That's why I intended to write another book after my first book with the original ending. This is prolly where most of my confusion is coming in...minus the jitters and freaking out that I could be done and all that jazz.

I'm just absorbing in advice here. I love reading your answers =D
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