You will be liable to pay interest and a fee for not filing the return on time. There is 18% interest per annum. The base for this interest is the amount of outstanding tax to be paid. It should be done from the next day of filing to the date of payment.
There is also a late fee, which is Rs.100 per day as per the GST Act. It is Rs.100 under CGST and Rs.100 under SGST, so the total is Rs.200. The maximum amount that can be levied is Rs.5,000. IGST is exempted from a late fee.