My mom forgot to include the Social Security on my parents tax return one year. By the time the IRS notifies them of the mistake, they owed penalties and interest, as well as the extra tax.
If you amend your return and send in any additional tax payment by April 18, you will not be assessed penalties or interest for the late payment. As noted above, you need to wait until your original tax return is processed and any refund that you claimed is paid before you can amend your tax return. TurboTax will probably not turn on the amending function until mid March.
