I think keeping an
error log can be very helpful if you take the time to review it and go over your mistakes. Just like anything else, you get out what you put in.
There are plenty of template error logs on this site or you can always go and make your own (not as hard as it sounds since you may not need all of the added features to the one on this site).
For my
error log, I had the source of every question as well as my answer and the correct answer (broken down into 5 separate columns for PS, DS, CR, RC, and SC). Then I would categorize the question by not only section (Ex. Geometry, Probability) but also by subsection (Ex. Geometry --> Circles or Probability --> Dependent Probability).
And then the last part (and in my opinion the most important) is your analysis of the problem. What was your thought process? Why was it correct / incorrect? Why is the correct answer actually correct? This is where you start to actually learn from your mistakes rather than just moving onto the next problem. Nearly every question (and every single one that you get incorrect) should have some sort of takeaway. Did you get the question wrong because you were careless or did you not know the material?
That is how you actually identify your weaknesses and then narrow down your studying. Doing problems is great, but if you are getting a lot wrong you need to identify what areas are your weakest and tackle the conceptual understanding. And even if you aren't getting many wrong, its important to focus on those more advanced topics to boost your score.