despite 700+ score in GMAT prep mock only 640 in actual GMAT

Assuming that you took your official practice exams under realistic testing conditions, the results show that, on a good day, you are capable of scoring higher than V30. Thus, it’s quite possible that nerves, stress, tiredness, or a combination of all three negatively affected your test-day performance. However, it’s also possible that you have some lingering weaknesses that were exposed on test day. Although I’m unsure of how you prepared, it’s possible that, in your preparation, particularly in verbal, you did not really learn to do what you have to do in order to score high on the actual GMAT. Rather, you picked up on some patterns that were effective in getting you relatively high scores on practice tests. So, for you to hit your score goal, your preparation, particularly for verbal, probably needs to be more complete, meaning that you have to go through the various types of GMAT questions carefully to find your exact weaknesses, fill gaps in your knowledge, and strengthen your skills.

For verbal specifically, you have to become more skilled at clearly defining the differences between trap choices and correct answers. Otherwise, you will get stuck guessing between two choices or be surprised to find that you incorrectly answered questions that you thought you answered correctly. Becoming more skilled in this way takes carefully analyzing all of the answer choices to lots of verbal questions to develop an eye for the logical differences between the choices. In other words, you have to go beyond answering practice questions and reading explanations to doing deep analysis of questions to learn to see everything that is going on in them.

In order to follow the path described above, you may need some new quant and verbal materials, so take a look at the GMAT Club reviews for the best quant and verbal courses.

You also may find it helpful to read the following articles:

how to score a 700+ on the GMAT

Why Was My GMAT Score Lower Than My Practice Test Scores?