Sometime you have to deal with IRS in the month other that April. It means that you received a dreaded letter from them, prompting to contact and setup an appointment.
Do not start to worry immediately and automatically. Most likely scenario is that some unusual percentage or number was caught by a computer, and it is now your turn to show some mathematical skills.
All you need to do is show that your numbers are all good and here is the way you arrived to your totals. Sound simple enough.