I'm facing a similar problem currently: I had been following my storyboard pretty much to a T for most of my comic, but since it's a one-shot and I was aiming for 50ish pages for the total length, when I got to the end of the storyboard and was exceeding 60 pages, I started rushing things to wrap it up as quickly as possible.
Now that I'm at the end of the story, I'm looking back and the storyboard and thinking like "wow there's no reason to arbitrarily rush the ending after coming this far" so as a result I've been having to come up with a lot of the content on the fly,,, designing a few chars that didn't exist at all in the storyboard, coming up with several pages worth of dialogue that wasn't there, etc.
For scope, I basically took what was two panels in the storyboard and converted it into 3 pages LOL and then there's 3 pages after those in the storyboard... which will probably end up being expanded up into 5-6 pages. Very uncomfortable creative process for me, I like having the storyboard to lean on