Tension. Stress. Fear of failure. Call it whatever you want. This is the biggest obstacle on the D-Day. While you should definately put in effort in strengthening your foundations, a small part of you should also be working towards stress management. Strategising your whole test by numerous simulations in actual test like conditions is an absolute necessity. Take atleast 7-8 full length tests before and along the way, get acclamatised to the actual conditions and hone your strategies.
In your specific case, what were your scores in your full length practice tests? If there was a specific trend you observed and your final score was way below expectation, which sections do you feel could be responsible for that? SC/CR/RC?
A test score needs a lot of retrospection. Analysis of what went wrong and how to correct it is as important as Analysis of what can go wrong next time (Guess work questions).
Over and over people in this forum have advised use, maintenance and continuous updation of
error log. I cant emphasise more, how important a tool it is for your preperation.
So, strategise your learning, plan your methods and equip yourself with the best tools - all of which are available right here.
All the best!