Yes, you have to file an amended return. The IRS gets a copy of the 1099-S, so they know how much you received from the sale. But they don't know that the home was inherited, and they don't know your basis, so they don't know that you had no gain. If you don't file an amended return to report the sale, the IRS will assume that your basis is zero, and that therefore the full amount that you received is all taxable gain. You have to file the amended return to show that you had no gain.
