June 6, 2019 3:47 AM
Yes, you do, for two reasons. The first reason is that you will get more money back. The second reason is that the IRS gets a copy of your 1099-B, and if you don't report it on your tax return, the IRS will assume that the entire gross proceeds are profit and they will send you a bill for additional tax, plus penalties and interest for failure to report and failure to pay. You can avoid that unpleasantness by amending your return and reporting the 1099-B.