How to pay GST shortfall

I file monthly gstr3b and as per bill I cliam ITC and remaining balance of tax I also paid but when I try to file GSTR 3B for the month of March 2020 then I see that my gst tax is less paid as per gstr2a and shortfall is 800 rupees. how it is possible and if this remaining balance of tax necessary paid then how can I paid this in the march 2020 return .