You like many others are thinking wrong. Take the person who got 78 mark in set 1- I'm sure he also made mistakes for 5-10 marks. So, the difference is mainly that, he made it from 90 mark range and you made from 60 mark range. While preparing for GATE one should target 80+. Every year marks are going up. As you told, you got more concepts this year, there are still more to get. Then there is time management, pressure handling, accuracy etc which matter. These are not so important in other exams, but for GATE you should really aim the top-- not average..