I Want To Start Writing...?

... But I feel like everything I write is just. Not. It. What to do? I've already written out every single detail; the plotline, the chapters, you name it. But every time I start writing the actual stuff, I feel like it's not good enough and erase everything and wait for inspiration to hit me again, one day... However, I don't want that! If I wait and wait, I'll never start. I've been working on this novel since 2008, so I don't want it to end without even starting it. Sure, I've written a few drafts, but the storyline has evolved and I can't look back. So, you guys have any advice you'd like to give me so that I'll be able to start writing? Thank you in advance!