Need to amend 2023 tax return I already mailed

[optca50]

I just mailed my tax return today and afterwards realized I did not include a dividend. 

Question 1: When I open Turbo tax to amend the return, the "federal tax due" says $311.  Why does it already have this amount before I have made any changes/amended the return?  Shouldn't it start at "$0"?

Question 2: Since I mailed the return today, how long should I wait before mailing the amended return? 

[JamesG1]

Are you saying that the $311 tax due is not what you reported on your Federal 1040 tax return that you mailed?  Please clarify.

Before you amend the Federal 1040 tax return, you need to be assured that the IRS has completed processing of your original tax return.   You will know that a mailed tax return is completed if you receive the refund that was reported on the tax return.

If you reported a balance due, you should refer to your tax account here to make sure that your tax return was processed.

[optca50]

No, I owed $40k to the IRS because I sold a house this year and paid the amount due with the filed taxes I mailed.

I went to the amend the return and the $311 showed up on the monitor at the top for "Federal Taxes Due" before I input anything to amend. There is "0" under State taxes.