I would say go with the flow if its your draft and do an outline during your editing process, things will change after your first draft. I'm currently going through the same thing where my characters hijack my story and do there own thing, i feel like this makes each character unique and different because its not me writing them, but the characters simply doing there thing like actors on a stage. Going with the flow can also lead to some moments in your story which you didn't intend and can make the story feel more organic than rigid.
