I would suggest you to stick to official material as much as possible.
If you have already exhausted official guide then consider solving it again. But this time start maintaining an
error log and practice the question in a timed way. Even if you get the question correct, see the official solution or search for an alternate easier solution on gmatclub
After you exhaust it take gmat prep practice test 1 & 2. Then search on this forum for "All gmat prep questions"
That is a huge database.
After that buy Exam pack 1 and attempt it. By this time you must have improved on quant big time. Re run the exam pack to solve all its questions too.
Even after this if you wish to improve or practice further, then buy exam pack 2
Once you get the hang of official questions and you just wish to work on your timing issues then take
Gmat Club tests and practive their 26 mocks.
I hope it helps!