Have you had a practice test to assess where you are?
You have not said that you want to get any kind of assistance like a GMAT course, but here is a response that I gave to someone who asked if they should take a course - it might help you to think about taking on the challenge ahead of you.
I generally give the following guidelines to people who have the same sort of question that you do - self-study or get some help.
1) How close are you to your goal right now? You say that you need above a 700. If you take a practice test now and you score within 100 points of your goal then you could get there in 3 months, if you are more than that distance away it could be tough on your own.
2) How much time can you devote to your studies? You have three months - to do it alone does take more time. If you can put in 20 - 30 hour weeks then you have a better chance of doing it on your own, or with books. If you are busier with work, and can only do something like 15 hours a week then you may be a candidate for getting some help. 12 weeks at 15 hours may seem like a long time, but it may not be enough to review all of the concepts and develop your own best techniques for each question.
3) Are you the kind of person who generally looks at something and tries to figure out the best way of doing it? If you plan your errands so that you have no left turns in traffic or so that you drive the fewest miles then you are a better candidate for self study. If you are a person who does better with some tips and techniques and maybe even a little more you might want to get some help.
4) How disciplined are you? Some people can set a schedule and stick to it. Others do better when they have a class coming up and they know the homework will be reviewed.
5) When was the last time you had a math class? The more you need to review the help you may need.
6) Time or money? It costs more to take a course (maybe $700 for an online course with books), but it takes longer to do it yourself.
Best of luck
