GSTR 3B rectification and liability payment

Dear all
while filing 3B for the month feb18, i missed out one sales invoice. verious post are saying that add your missing details in upcoming 3B that is for now april 18 as i have already filed both feb n march. can i add feb sales in april 3b and pay off the liability ? what will be the position at tym of GSTR 3 as it will again ask me to pay tax for the month of Feb ? should i wait for GSTR 3 ? Plz guide