TurboTax is being idiotic, trying to file a state return as Nonresident after I told it Resident. Can this be fixed?

Yes, it can be fixed. If you haven't submitted your state return yet, you can go back to the beginning of the state interview and change your residency status.

This is how to do that in TurboTax Online:

1. Open your return.
2. On the Home screen, scroll down to State Taxes, and select the down arrow to the right.
3. There'll be a status in the section you expanded. If it says Submitted, you will need to wait until after your state return is accepted or rejected, and may need to file an amendment to correct your filing status. 
4. If you have already submitted your state return, see more about amending it.
5. If you see a status other than Submitted, click on the status box.
6. Select State Taxes from the left-side menu, then Your state returns.
7. To the right of your state name, select Edit. 
8. On the next page, select Edit to the right of General info.
9. Review the remaining questions about residency status and make any needed changes.

Please note that the questions you see vary based on your state and the answers you provided in the My Info section. 

If you don't see an option to select Resident instead of Nonresident, you will need to review the answers you gave in the My info section. 

If this doesn't help you solve the problem, ‌respond back with more information, including the state you are working on whether or not you still live in that state, so that TurboTax can help you further

 

BUT....if you moved states during the year, a couple states use the Non-resident tax return to allocate $$ received between the states......or sometimes give you the choice to file as a Resident or non-resident.

MO and SC I know do this, perhaps a few others.

Most states just have special part-year resident tax return forms.