I'm American and yesterday I realized I made a mistake on my taxes less than an hour after I filed them. Some googling told me it's not a huge deal, just have to file an amended tax return after my initial one is accepted but I can't ignore it because the IRS will know I did it wrong because they will have received a form from another party with the numbers I forgot to put in. It's baffling to me why it's a weird negotiation to pay taxes instead of them just telling me what I owe since they do know what I owe.