Final Trust Return

It's not all that critical but you should go ahead and do it. 

Just print out the exact return you filed previously, mark it final and amended, and then print and mail it. Attach an explanation to the effect that your original return did not have the final box checked.

Yes, you can file an amendment for your Form 1041.

You will prepare a new Form 1041 with the correction (final return checked) to amend your Trust return. Also check the amended return box at the top of the form and make sure that you mail a copy of the original return with it. You can attach an explanation that the original didn't have the final return box checked.

@SD2025