You would think so, but the great American income tax system is too complicated and convoluted for simple straight forward answers like that. Critter#2 has identified one item: they may be trying to charge you self employment tax. This is usally a problem for a 1099-Misc with an amount in box 7. But the IRS will frequently assume a box 3 amount really belonged in box 7, particularly since you reported it as wages.
Are you eligible for the Earned Income Credit (EIC)? More wages would indicate either more or less EIC depending on where you fall on the EIC curve.
What does the rst of the IRS letter say? They are usually specific about which calculations they used.
