Fixing Corporation Tax Error

Last year May15-Apr16 was my first year of trading and I happily raised bill ( to correct account) for Corp tax due in Dec17 when the payment was due... Having got to year 2 and read the instructions I am guessing I should have dated the bill for HMRC as due in last tax year 15-16 -

System now shows last years corp tax payment in P&L in Dec 16 . Will I muck the system up if I void that old bill and re create with a due date in the old tax year.

Assuming this is what I should do ?

Any help appreciated