Provisional Tax - what Provisional Periods should I be using?

I submitted my 2015 tax return [regular tax return] for March 2014 to February 2015 period, by due date in November 2015. No problems and monies due paid over. I subsequently discovered that I was supposed to have submitted as a Provisional Taxpayer, not as a regular taxpayer. I now have to do another tax return, due 29th January 2016 [today!!]. I am registered as a Provisional taxpayer now but am unsure as to which Provisional period I am supposed to be choosing from the list that pops up. Should it be 2015, Period 2, or should it be 2016, Period 1? Also, do I declare last 6 months earnings only or last 6 months plus the upcoming 6 months [estimates]. How will this crossover from regular taxpayer to provisional taxpayer affect monies owed or due? Your advice will be very welcome.

The tax return today is the one for the period 1 March 2014 to 18 Feb 2015 so you have already submitted your tax return. The next tax return is due 29th Feb 2016 which is the 2016 period 2.