How organized are you talking? Of course, the only way to have your story 100% organized before drawing is to not draw it until you finish all the writing.
From what I gather, you have an ending for each chapter, but nothing more detailed in your outlines? I would at least have a workable sequence of scenes leading you from beginning to end (that you can still tweak if need be). I'm talking at the level of "scene 1: X happens. scene 2: Y happens etc".
If you want to go a bit more detailed, draft out how the scenes actually play out. Don't worry too much about wording things exactly right; you can figure that out when you get to drawing, otherwise you might as well just write the entire thing out like I mentioned at the beginning XD
If it helps, I've divided my entire comic into 5 'sections' each with its own ending; I've got my workable sequence of scenes for my first 3 'sections' and my detailed drafts are I think about 3 scenes ahead of my art :]