@Capage- don't give up and don't give GRE just yet. I am not an expert but I had a very similar experience.
I was in your shoes. I had studied for two months solid. I score 510 on my first timed GMAT prep test. And I feel you. You go like "Really?" In fact I got nervous missed the last few questions badly. I knew the 510 was not my score. So three days later, I took a Veritas prep test and scored 540. Another 3 days later I scored 570. Then I stopped taking tests. BIG MISTAKE. I was improving. I was learning the real thing in a timed environment. After 10 days I took GMAT prep test and scored 560. At this point, I stopped taking tests for a day and reviewed all the questions making notes where I went wrong, where was a timing issue etc. Last week I took three practice tests. I scored 570 on two and 590 the night before the exam. G-DAY score? 640 (q43, v35).
I am underscoring the importance of proper study. We all know that. But I am emphasizing the importance of practice exams. Try taking 7 of these and analyze all your mistakes. You should be in good shape. I speak from experience. Oh, on a side note, there a book by Brandon Wu. it is about scoring 780 in 30 days.
https://www.amazon.com/30-Day-GMAT-Succ ... B009ZNCOGQWhile this does not happen every day, nonetheless one of the key lessons is spending more time on practice exams then even content. Hundreds of people have used his book to succeed. Just food for thought for you.
Best of luck!