Yes, it is possible to add self-employment income (after e-filing); you will need to file an amended return.
Wait for your return to be processed by the IRS before amending.
See FAQ below
to Amend 2016 Online:
https://ttlc.intuit.com/replies/5567856
See FAQ below
to Amend 2016 in Desktop:
https://ttlc.intuit.com/replies/5114143
