Although it’s very important to have an idea of your story’s structure before actually doing any writing, you also want to allow for the story to unfold organically and naturally, and the only way to do that is to give your characters some breathing room. Rather than forcing your character into an arc and dictating all of their actions, try to let your character make their own decisions that will move your story forward.
As you write any given scene, ask yourself how your character would react to the circumstances they are in. Don’t think about what you would do.
So go into your scenes and story with an open mind, especially in early drafts. Don’t get too hung up on having a perfect character arc in the first draft. Let it unfold naturally, and in later drafts you can go back in and highlight the arc more, once your character has shown you what it really is.