like the above says it's normal not being able to cover every detail in your story, especially not right from the start, but having outlines and personal notes to keep all your info organized will help
in animation (and probably other industries as well) i've seen folks organize what's reffered to as a show bible which has all the info about the story, worldbuilding details and other notes that may be relevant so that as you progress with the writing and storyboarding you can reference that bible to add in or flesh out and show details through your story telling
obviously it's gonna take time and may not be easy, especially if this is your first story, but focus more on just doing what you can and trying your best. besides it's often told to newbies that while your first work may not be "perfect" what matters is just kind of enjoying the process and using it as an opportunity to learn till you make the next one or just ask you go depending on length of the first one