hi Raysaranya,
I am also preparing for GMAT now, but here is my 2 cents. Did you maintain an
error log to understand why scored only 64% on SC on the OG. Ideally the score should be higher. You should first find out where you weakness lies. is it understanding grammar (is it idiom, modifiers, S-V) or is it just understanding meaning of the sentence.
For RC, go through the below link, this person had a similar issue, he has detailed how he overcame RC.
650-to-750-a-10-month-journey-to-the-score-203190.html#p1558631For DS (or anything Quant), you have to follow the math genius bunuel and his threads (see the key one below). Also there are some tips on DS too in the above link (like Empower)
all-you-need-for-quant-140445.html#p1130136But did you actually practice OG quants. If you have done that, you can try
gmatclub tests that are best, but if you dont want to buy a separate package, then please find other materials in bunuel's link above.
Thanks,
---Kudos if this post helped you---