I just got back from teaching/taking pitches at my fourth and final conference of the year, the Women Writing the West Conference in Tucson, and was struck during pitches at how many writers had completed works but hadn't yet started sending out queries. In some cases, they'd been sitting on the book for a year or more or even moving on to work on other novels.
Don't do this. You put a lot of work in finishing that book, and even if you're consumed by doubts, you need to give that book a fair shot. You may be telling yourself it's not quite ready, it needs another draft, you have to polish your query, or any of a hundred other excuses, but all you're doing is denying that book its fair shot. And yes, I accept that the book really might need another draft, a polished query, or whatnot, but that just means you're procrastinating at an earlier stage, probably out of fear.
The truth is that we're often not the best judges of our own work. We're too close to it, too aware of its flaws in some cases, and too blind to them in others. We remember the creation process, and we remember how ugly it looked during certain drafts, or how contrived it seems because we remember inventing it out of whole cloth.
None of that matters. Your book needs its fair shot. Worst case scenario, it's not ready and gets rejected, and then what are the consequences? Nothing. You've taken a few rejections, just like everyone else, and you're still free to revise that manuscript again, or, better yet, to mentally let go and focus on the next project.
Here is a great little clip by Derek Sivers giving some similar advice. https://www.youtube.com/watch?v=xcmI5SSQLmE