I think my challenge is both. When I study, I can do a lot of the OG problems, but on the exams everything looks different. Honestly, I feel like most problems I see on the exam are completely knew and different than what I studied. Is there a possibility that I need an extensive background in math first to do well on the GMAT?
Of course the real GMAT problems will be different from the OG. These questions are retired ones and will never appear in an exam again.
Your score says that you lack basic fundamentals. For your budget you can easily purchase an entire ManhattanGMAT kit comprising of 8 guides, OG + 2 supplement plus basic strategy supplements and online material. I feel that this kit is sufficient to score a 650! You should check it out.
GMAT done - a mediocre score but I still have a lot of grit in me
The last 20 days of my GMAT journey