If you aren't scoring at the level you want to score right now, then you do need to do something differently. And just practicing more problems without actually changing your approach is not different.
You can improve any of the three (including RC), but most people find that RC is the hardest to improve and / or takes more time than the other two question types.
It sounds like you've already got a plan for SC. For CR, you need something similar - identify a source that teaches you how to break down and analyze CR arguments and question types. I'd ask around here to see what people have liked and take a look at Eric's blog to see what he used.
A month might be enough time or it might be a little bit short - it really depends upon how much CR tends to be a strength or a weakness for you, and how easy or hard it is for you to learn the lessons in whatever book / program you choose.
Also, re: OG, if your score is not where you want it to be, then you aren't done learning everything you could from the OG questions. At this point, your study should not be about just doing a bunch of new questions - your process is already problematic, so you'll just be reinforcing the mistakes you're already making. Learn how to approach CR from the ground up and pick apart those same OG questions to see how the approaches work depending upon problem type - analyze those questions, don't just do them!
Of course, it doesn't hurt to also have additional new questions to do. I assume you have used all three of the current OG books? The next place I'd check is OG 10th edition. This has about 75% overlap with the 11th edition, but 25% of the questions are different. Basically, you'd just start using the book and if you hit something you remember, you can just skip it. If you hit something you don't recognize, it's either new or it's something you've forgotten (so, it's like new). The 10th edition is out of print, but I think you can find used copies for around $10, or you can see whether your local library carries it.
You can also order old paper-and-pencil tests to get more new, real questions - but do NOT take these tests and grade them and expect them to be a good reflection of the CAT. The old test functions VERY differently. Use the questions as good individual examples (or make group drills out of multiple questions) but don't use them as actual tests.
