Is Interest payable on unpaid GST liability or unpaid Net Cash liability?

Dear Experts,

In the GSTR3B of November, 19 there is unpaid GST of about Rs. 20000 due to miscalculation of sale invoices. At the time of filing I had enough ITC balance to pay the correct GST liability. Should I pay interest @ 18% p.a on the unpaid GST amount in the GSTR3B of December, 2019 even if I have enough ITC balance to pay the extra unpaid GST liability at the time of filing?