Ask HN: How do you 'finish' your projects?

So here's my issue. It's a long standing issue that I've always had, but has never really been an issue until now. I was given a big project for a big company for a big eCommerce platform. The extension I wrote will soon be released to the masses for consumption and use.

Now here's the problem. I keep looking at the code and trying to find bugs, add more little snippets of validation, etc. I keep finding ways that I can make parts of the extension better in some way. All the code is completely commented and I keep finding ways to make the thing better (or at least I think I am).

Does anyone else ever do this kind of thing? When do you say it's "complete" and move on to the next project? This extension works and works well, and has been tested all kinds of ways. I'm not the type of person to half ass a project and this is for a very large company and I really don't feel like making the company I work for nor my self look bad.