Why do I need to fill out Schedule C on my 1099-NEC form when I am not self-employed or own my own business? I was only paid a one-time fee for my services of writing

To enter a Form 1099-NEC that is not for self-employment -

Click on Federal
Click on Income & Expenses
Scroll down to Other Common Income 
On Form 1099-NEC, click the start or update button

Or enter 1099-nec in the Search box located in the upper right of the program screen.  Click on Jump to 1099-nec

On the screen Did you get a 1099-NEC?, click on Yes
On the screen Do You Want to Enter Your 1099-NECs Now?, click on Add a 1099-NEC
On the screen Let's get the info from your 1099-NEC, enter your information and Continue
On the screen Describe the reason for this 1099-NEC, enter a reason and Continue
On the screen Does one of these uncommon situations apply? -

Select This is not money earned as an employee or self-employed individual, it is from a sporadic activity or hobby and Continue

The amount entered from the Form 1099-NEC will be entered on Schedule 1 Line 8z
The total from Schedule 1 Part I Line 10 flows to Form 1040 Line 8