Yes, you can revise your income tax return with tax audit. The revised due date for the same is November 30, 2020. However, please note that a penalty may be levied under section 271B. The minimum penalty that can be charged is 0.5% of the total sales, turnover, or gross receipts. The maximum penalty applicable is INR 1,50,000. A penalty can be avoided if the taxpayer provides a reasonable cause for not having the accounting records audited.
Further, yes non-speculative losses can be set off against FD interest income and you can claim a refund of the excess tax paid. Hope this helps