It is probably working to your advantage to timely amend your tax return even if it means you have to pay more tax than your original filing is for. Here is IRS's tips about amending your tax return.
From
IRS:
You’ve discovered an error after your tax return has been filed. What should you do? You may need to amend your return.
The IRS usually corrects math errors or requests missing forms -- such as W-2s or schedules. In these instances, do not amend your return. However, do file an amended return if any of the following were reported incorrectly:
• Your filing status
• Your total income
• Your deductions or credits
Use Form 1040X, Amended U.S. Individual Income Tax Return, to correct a previously filed Form 1040, 1040A, 1040EZ or electronically-filed return. Be sure to enter the year of the return you are amending at the top of Form 1040X. If you are amending more than one tax return, use a separate 1040X for each one and mail each return in a separate envelope to the IRS processing center for the area in which you live. The 1040X instructions list the addresses for the centers.
The Form 1040X has three columns. Column A is used to show original or adjusted figures from the original return. Column C is used to show the corrected figures. The difference between the figures in Columns A and C is shown in Column B. There is an area on the back of the form where you explain the specific changes being made on the return and the reason for each change.
If the changes involve another schedule or form, attach it to the 1040X. For example, if you are filing a 1040X because you have a qualifying child and now want to claim the Earned Income Credit, you must attach a Form 1040 Schedule EIC to show the qualifying person's name, year of birth and Social Security number
If you are filing to claim an additional refund, wait until you have received your original refund before filing Form 1040X. You may cash that check while waiting for any additional refund. If you owe additional tax for 2005, you should file Form 1040X and pay the tax by the April due date to avoid any penalty and interest.
Generally, to claim a refund, you must file Form 1040X within three years from the date you filed your original return or within two years from the date you paid the tax, whichever is later.
