How difficult is the GD-PI round at IIM Ahmedabad? What exactly happened and how did you prepare for it refer to the details?

Yes, it is extremely competitive, particularly in the GD at IIM Ahmedabad. You would now have WAT (Written Analysis Test).

You should prepare for GD by reading 3 to 4 topics per day, reading magazines and newspapers, using the internet, and taking notes in a notebook. Draw diagrams and try to construct a thought structure for each topic. This approach should be useful unless and until you are a voracious news reader/consumer. And, yes, keep a physical notebook. Prepare all common questions for PI, such as Why MBA, Tell Me Something About Yourself, and so on. Perform some mock interviews. If you can get your hands on some alumni, conduct mock interviews with them.

For all call-getters, IMS organizes an Achievers' Workshop (with some consent to claim your credentials, if you get selected). Mock interviews are conducted by IIM (including IIMA) alumni during the IMS workshop. Mock interviews are essential; conduct at least three to four over the course of a month to improve your interview skills. Do your own soul-searching and plan your responses before the mocks. Structure implies having a reason for saying what you said.