@singltw
Since you owe on your original return, and your original e-filed return has been accepted, you can go ahead and amend your return.
Your scheduled payment should be unaffected, but you can call IRS e-file Payment Services 24/7 at 1-888-353-4537 to inquire about or cancel your payment. Please wait 7 to 10 days after your return was accepted before calling.
The IRS advises in What taxpayers should know about amending a tax return that taxpayers with a refund on their original return wait for the refund before filing an amended return, but makes no similar suggestion relating to amending a balance-due original return.
[Amended 2/10/2022 | 4:57 am PST]
