Dude 390 and 700 is a totally different world. Almost everyone without preparation can get 400 but 700 is not the same.
Many people have been spending many months to increase their scores from 650 to 700. However, many of them could not make it. Your score is 390 which is not a good score for any business school. Let’s be realistic here, I suggest you to aim for 650 first. If you can make 650 then 700 is possible. (you know only a handful of people get 700 or above)
However, if you really think you have the potential to reach 700 I am not going to stop you but all I can say it that it is not going to be easy.
Your friend,
BB