Interest rate for GST

I wants to pay liabilities of April to June....... actually I have mentioned sale bills in gstr1 of April to June month,but file 3b of these as nil retun....... I wants to pay this liability

pls suggest me ....

1.

should I have to file gstr9 and pay liabilities there.... if then what's is the interest rate

2...can I file DRC in January month to make the pending liability of April to June... that I have already mentioned in gstr1