Have you updated the outline of the story? Doing so will give you guidance.

How's the outline coming?

I use spreadsheets for outlines, time lines, character flow relationships, appearance,...

Spreadsheets are the best writing tool.

We writers are the only people who like to constantly paint ourselves into corners. Especially when we are in cylindrical rooms. The trick is to see it as a challenge. Perspective helps. Take a step back and look at the accident from a bird's eye view, instead of under a microscope. Ask yourself, "if I leave it this way, how will it effect the rest of the story?" Sometimes, especially when all you have is a vague idea about where the story is going, it actually helps to complete the story. Accidents are great in the fact that they allow you to surprise yourself. And, worst case scenario, you don't like it and have to tweak or rewrite a chapter. Personally, I love painting myself into corners and then thinking my way out of them. In what I write, that is. In real life, not so much... lol.

Your characters may be writing themselves but you have the final veto, see where they take you and change it later if you want to.

My guiding principle is this - I don't write my characters, I simply take dictation.

The best moments of my writing has been when I have been laughing out loud - I shit you not - that my characters do things I don't expect. Embrace it. It has worked out for me. For the princely sum of $2.99 you can download my novels - and, man, they went in ways I did not expect.

So my advice is not only don't sweat it; actually use it. Because you can't make characters do something that they would not do. It's an organic process.

My feeling is - follow your characters. My novel 'The ladies' Suicide Club' didn't turn out at all as I had originally planned. My characters took on a life of their own and I had the same experience as you - they seemed to want to create their own stories. Write whatever happens. You can go back and rewrite when you have the first draft done. You may find you want to change a lot or you may find you like it the way it is. Keep going!

This what first and second drafts are for, don't hold yourself back, let it all out and go where it will, you might find stuff you write now for this book that has to be edited out, will be perfect for a story ten years down the line.

Sometimes, one has to rewrite, if the problem will require too much stretching of credulity, but keep a copy, because there are two possibilities. Either remove the events leading up to the comment, and make slight adjustments, or keep the comment and do a major change of later events. Sometimes, this can lead to the plot of a second book. I tend to read what I have written, then go to bed. When i wake up, after a snooze, I often have a brainwave.
However, I have never published a full length story myself. I ran a publishing business and wrote short stories and articles, etc. I do help a published author dream up plots and situations, and then edit her work.