Hello Subarao,
There is absolutely nothing to worry about the low scores you have received in kaplan tests.
Infact i never got above 650 in kaplan but ended up with 770 in real GMAT. So dont waste time in analyzing why you got less marks in test. Instead go through the wrong ones and if you still have any doubt, post it on this forum and discuss it with your forum buddies.
I found kaplan's math really easy. It can never be so easy on real test. Pay more attention to verbal section.(of course, all this only for practice)
As advised by rawjosh, get yourself registered for GMAT and download
GMATprep ,give one test and see where you stand. Nothing comes close to the
GMATprep.
Goodluck