Hi there,
There are many aspects to your performance and your way forward. Firstly, and most importantly, please recognize that you have not done badly! Obviously, the score you have received is not the one you want but it is clear you have a foundation. If there were no solid foundation, there would be a problem.
In terms of practical advice, it is certainly ok to relook at the test prep questions and the official guide. But beforehand, several other things need to be done and determined. There has to be a good analysis of where your weak and strong points are. For example, in the Verbal section, and even within the Sentence Correction questions, it would be important to know what the trouble is exactly.
Therefore, proper techniques for all question types is crucial of course. Even within the critical reasoning, each question type (for example Assumption versus Inference versus weakening, etc) has, or should have its own technique and your job is to become very familiar with what you are faced with. So, for example, if you see a verb in the Sentence Correction, immediately you must know to check for things like Agreement with Subject (of which there may be a few types), Tense/Form, and Parallelism. The more automatic you become the easier the exam will be. They wish you to overthink everything. Your duty is to say, "I know everything here because I have learnt it and seen it several times- it is repetitive!" One of the most important things you can do once you learn how to attack every question type properly is to also take several practice exams and do much self analysis. The fact that you get something correct is not interesting from a learning perspective, but the fact that you make a mistake...now there is something to chew on as this gives you a clear idea of what is going on.
In addition, questions of time strategy come up. Where did you spend a lot (too much?) time; did you finish the sections comfortably; are you sacrificing several questions because you spent to much time on 2 or 3 questions that are designed to waste your time, and so forth.
Think of this as a holistic approach to your studies,. Not only do you need to utilize proper technique in a very consistent manner, but you must also make sure that your timing strategy works AND that you are fully confident, which you should be. Again, if you had received a 300 after much studying, this would have been a red flag, and I would still have encouraged you, but the fact that you are scratching the 600 tells me that you are decent but have the ability to improve as well.
Good luck! There is no doubt you will improve.
