GMAT Strategy

When it comes to improving in math, I believe that you should compartmentalize your learning and take the time to master each topic (e.g., percents, ratios, exponents, statistics, etc.).

This means that, for each topic, you should:
1) Learn the underlying concepts (rules, attributes, notation, etc.)
2) Learn GMAT-specific strategies related to that topic
3) Practice dozens of questions all related to that one topic.
4) Don't stop working on that topic until you have mastered it
Then, and only then, move on to the next topic.

I also suggest that you spend a lot of time reviewing the responses from the Experts on this site. They model the steps you should be taking when tackling math problems.

Cheers,
Brent

I think that, as you progress through the various topics, the improvement in your mathematical abilities will help to increase the speed with which you complete each subsequent topic.

You still have 3+ months - that's lots of time! In fact, since you have 3+ months, you might consider signing up for BTG's free 60-Day Study Guide (https://www.beatthegmat.com/mba/gmat-guide).
This will help keep your studies on track, and ensure that you will cover everything that the GMAT tests.

Cheers,
Brent