That is correct, your "additional" federal tax and "additional" state tax amounts are automatically added to the amounts in boxes 2 and 17. One way you can confirm this is by looking at your first paycheck stub of the year and comparing the figures in the year-to-date column and current pay-period column. The combination of federal tax withheld and "additional" federal tax withheld for the current pay period, on your first check of the year, should equal the total of federal tax showing in the year-to-date column. The same for the state taxes and "additional" state taxes. The other way to check it is to manually add the taxes withheld on every pay stub for the year and compare with the amounts reported on your w-2.
