Hi Ananta
That diagnostic test is kinda hard! I did that before beginning
OG prep and got pretty dismal scores first time round. I would just like to say that in general its the timing on this exam which really makes or breaks you (i've written it twice already and am going for a rewrite).
One indicator, as you've mentioned, for your low timed score might be that you're concepts are weak. That means you should figure out what topics you are particularly weak in, buy/find targeted supplemental material for this (or consider a prep course, bb always mentions one with a money-back guarantee), and target you weaknesses.
I would recommend that if your timed questions are going badly, taking a step back and analyzing what the overall problems are is not such a bad idea (what I've been doing for the last 3 months too). Don't blindly launch into more timed sections without covering the basics! I made this mistake last two times. It will require a meticulous prep schedule from you.
Try a study plan where you've highlighted topics you're weaker at, you do a chapter on a specific topic, practice the questions corresponding to it (NOT under timer to get the concepts right), THEN practice the
OG questions/other questions under a timer. See if that helps!
And no offense, but I would not go the Kaplan way. But that's just me.