Hi Apurve,
Test Day is a rather specific 'event' - the details are specific and they matter, so you have to train as best as you can for all of them. The more realistic you can make your CATs, the more likely the score results are to be accurate. The more you deviate, the more "inflated" your practice scores can become - and that's what happened here. By skipping sections, taking the CATs at home, taking them at different times of day, etc., you weren't properly training for the FULL GMAT 'experience.' By extension, your practice CAT scores were not accurate.
I'm hoping that you can clarify one of your answers. Since this was your 3rd Official GMAT, are you saying that you did not use those 4 Official practice CATs while you studied for either of your prior 2 attempts? In addition, are you saying that you never saw any of the questions from those 4 CATs during your studies (not even working through questions in the Forums here)?
Beyond the inconsistencies in how you took your practice CATs, there are some other possible factors that could have impacted your performance, so I have a few additional questions about the lead-up to Test Day and Test Day itself:
1) What did you do in the 3 days before your GMAT?
2) How did you sleep the night before your Test?
3) How long was the ride to the Test Center from your home?
4) Were there any distractions at the facility or during the Test?
5) What did you do during the two 8-minute breaks?
6) Did you finish any sections early?
7) Did you have to rush to finish any sections (and guess on questions just to finish on time)?
GMAT assassins aren't born, they're made,
Rich