It’s possible to get any grade in a month (and a month and 3 weeks - even more so). In general, the optimal amount of time to study for the GMAT is 6–8 weeks, or more accurately 100 to 120 hours spread however which way - provided you study right. But what does ‘studying right’ mean? The mistake many people make is substituting quantity for quality. Many people study more than this (3–4 months) but this isn’t necessarily better - if we study too long we can start to forget what we learnt in the beginning.
I suggest starting off with making yourself a study plan, consisting of these steps:
Familiarize yourself with the exam – What is the test structure? What are the formats of the questions?
Focus extra practice time on your areas of weakness – What matters is getting to the correct solution, fast: the problem is that just solving lots of questions (with practice tests or coaching) is not sufficient in terms of improving mental flexibility. Actually, the opposite is true. Solving thousands of questions without improving your mind’s flexibility will only cement the wrong thinking patterns.
Train yourself to find YOUR best solution approach to answering GMAT questions – The GMAT measures your ability to flex your mind. There is often more than one way to get to the correct answer - the trick is figuring out which is that way that is FASTEST for you.
Researching your errors is even more important than solving new questions – Which tools am I using betters than others? What are the main reasons for my mistakes? Which other tools should I learn to apply better? And when it comes to verbal questions, it is also crucial to analyze the answers: why is the correct answer correct? What is wrong with the wrong answers?
Practice test should be used as tools for improvement, not just to see “where I stand,” which means that you should allow 4 hours of research for every test, and not take two tests in one day, one after another, so as to allow yourself some time to strengthen your weaknesses and prepare for your next opportunity to improve.
As you still have a month to go, you might want to consider trying online computer assisted customized learning. What does this mean? Instead of reproducing the teacher-in-a-classroom experience online, a site like this uses personalized machine learning to bring the best out of each student. By monitoring thousands of other students who are tackling the same question as you, the site can provide you with the approaches that proved most efficient for each given question.