Thanks all for your advice (& reassurance!)

I am going to try a multi-pronged approach. There are definite pieces that are missing from earlier in the story (it's SF and there are things I just plain forgot to explain (or illustrate) that will make no sense otherwise). And there is at least one occasion where my outline says "insert complications" that I....forgot to do. As well, there is a character who has been hanging out with my MC & friends who would be really better off having her own story thread.

I know a little about what is going to happen in the sequel, and if I finish this story I will start on that.

Part of the reason I am disappointed is that I was using NaNoWriMo to force myself to actually complete a novel (not something I have accomplished yet), and if it turns out this is actually a novella I still won't have accomplished that.

Okay, back to writing...