Capital gains

Dear Sir, March 2010: I purchased an under construction property & registration was done in march 2010. At the time of registration appx 35% of flat cost had already been paid to builder. Till September 2012: appx 90% flat cost had been paid to builder. Due to delays etc Flat was handed over to me only in Dec 2015 ( ie .more than 3 years after 90% payment was made). Balance to be paid, appx 10 % of flat value & one time maintenance corpus & car parking ( Appx 6 % of flat value) was paid to builder AT TIME OF POSSESSION ( DEC 2015). My Question is: 1) As agreement was done in 2010 march, but possession given only in Dec 2015, IF I SELL MY FLAT today then capital gain period will be counted from march 2010 or from Dec 2015?...ie transaction will come under short term or long term capital gain? 2) As 90% of my payments have been paid more than 3 years ago ( ie by sept 2012), then how can that come under short term gains? IF at all, i should only be liable for short term gains on 10% of final payment made in dec 2015. pls adv