How did you report your self employment income? Did you fill out Schedule C? If you had a Net Profit of $400 or more Turbo tax would automatically calculate the self employment tax. Check if you have Schedule SE for it and 1040 Schedule 2 line 4 which goes to 1040 line 23.
If you didn't get Schedule C or pay SE tax you need to amend your return. The SE tax is in addition to any regular income tax you owe. How did you get a tax refund? Did you have withholding taken out of your Social Security? Or pay in extra estimated payments?
By reporting self employment income it counts towards your Social Security benefits and might increase the SS checks you get.
