Short Payment GST.

We have paid GST liability of Rs. 80,00,000/- in the month of July'2017 by generating payment challan through GSTN portal.

But, we have shown GST liability of Rs. 78,00,000/- only on Form GSTR-3B by bymistically.

Hence, we are required to show short GST liability of Rs. 3,00,000/- in the GST return and want to pay.

In this case where are we show above mentioned short liability in GST return in current month?

Please advice.