The IRS will send you a corrected tax return, you sign it and mail them a check and you'll hear nothing from them again. Maybe you didn't get the form, or didn't understand the software, etc, etc. There are lots of honest ways to screw up your taxes. The IRS isn't going to assume fraud unless you refuse to pay them when they point it out.

I've screwed up my taxes a lot of times. Not maliciously, but not having all of my forms, I've had clients report paying me a different amount than they told the IRS, forgot stock trades I made, etc. Every time, they've sent a letter asking to pay a balance, plus maybe a small fee, and all is good.