hey What on earth made u give GRE in such a haste.
Now that u have only 20 days... i would advise u to go thru HIGH FREQUENCY words in barron's ... atleast to get familiar with verbal.
N hope ur inherently good at Math cos u really dont have time to improve ur skills at numbers.... still go thru once again Barrons.
N try making it a point solving ETS CD which must have been sent to u by now .... it does help. If u dont have one try getting it frm someone.
N keep ur coooool.... its will not help if u get stressed out.
All the best.