AFAIK the IRS has historically been more, er, disinterestedly nitpicky as opposed to disproportionately vindictive.

More "you say X we say Y here's your options you are Z days over with a W% rate", rather than "Ah hah! $50 dollars error, time to make an example outta this poor bastard."

Generally, yes. If you make a mistake in your return, the IRS is perfectly happy to accept an amended return, and you pay (or get paid) the difference (perhaps with a penalty fee). They usually only go after you criminally if they think you committed fraud.