The IRS will let you know what they think you owe. They will tell you why. And, AFAIK, tends to waive fines if the mistake was honest and quickly corrected.
Wow that's nice. In Holland the government always assumes you did it on purpose even though usually that isn't actually the case.
This was my experience too. While it takes a good long while to get resolved, because my mistakes were accidental and I talked it through and followed the process, I was dealt with politely and given grace.