@jnrgarbutt - Normally an amount in box 3 is not self employment. But the TurboTax (TT) interview is designed to aggressively see it if it really is. You answered the questions in a way that TT concluded it is self employment.
What did you do to get this money. Any sort of labor or service (work) is considered self employment.
Yes, you are taxed twice. You pay regular income tax and you pay self employment tax (social security and medicare tax about 14%)
