I do not own my own business. I helped assist at a busy time for a few hours in a friend's business and received at 1099-NEC. Do I have to file as self employed?

You are a sub-contractor which is business in the IRS eyes.   

You do not have to carry on regular full-time business activities to be considered self-employed. This is non-employee compensation.  You were contracted to do a job, not employed to do a job.  You will need to file a Schedule C for Business Income and Expenses and pay Self-Employment tax on this income. 

To file a Schedule C, here are the steps: 

1. Sign in to your account and select Pick up where you left off 
2. At the right upper corner, in the search box, type in schedule C and Enter  
3. Select Jump to schedule C  
4. Follow prompts