upload the invoices in april month's gstr 1 and also include the turnover in the same month's gstr3b and pay interest at the rate of 18% p.a . then it can be shown in annual return. in order to pay tax turnover has to shown in gstr3b. so my advice will be to show the turnover in this month's gstr1 and 3b
GSTR 9 cannot be filed without filing all GSTR 1 & 3B's of that FY.
If the said returns are filed and just few invoices are not disclosed - pay the liability through DRC 03 (since adjustments related to FY 17-18 cannot be disclosed now as due date has been lapsed - 31st Mar'19)
If the returns are not at all filed - Returns are to be filed 1st (ITC cannot be availed now)