Nitwick Don't pay much attention to the absolute scores that you receive on the unofficial CATs. The 650 on the GMATPrep is a good place to be, of course you need to push yourself from this point, but don't obsess about the 580, it may not accurately reflect where you currently stand. In fact, I have seen such massive variations in unofficial CATs that I tell students to ignore the absolute number and only use them for getting used to taking full length CATs. If there was more time, I would have recommended you to take the Exam Pack 1 tests to get a sense of where you really stand, but at this stage they will not be useful.
The only advice I will give you is to not be fixated on the first 10 questions, sure I want you to do the best on those but if you see a hard question, please let it go. And by that I mean a question that you are not able to understand or where you have not made any progress in say a minute or so. This will help you balance out your overall timing and you would be able to do justice to the questions towards the end, which are also important.
Best wishes for the exam.
Dabral