I am constantly checking and re-checking my work. Often I find errors, so then I fix them. Then I leave it on a shelf for 6 months. Then I check it again. So, yeah. When will my story be done? It’s gonna happen sooner or later. Definitely.
It doesn’t matter whether this is your first manuscript or your fifty-first. It doesn’t matter whether the recipient is your first mentor or the agent of your dreams. It doesn’t matter whether you’re writing a contest entry, a novella, a full-length novel or a trilogy. At some point you have to decide:
Yep, this is ready to send.