Hi aditya1422.
It's actually pretty common for people to experience a drop from their practice test verbal scores to their actual verbal scores when they take the GMAT, and there are a few possible reasons for such drops.
One is that they simply had an off day.
A second is that, when they took practice tests, they had already seen some of the verbal questions on the test because they had used them in their practice sets on GMAT Club or in another resource.
Another is that they used GMAT prep resources that included questions based on the questions in the official practice tests. So, they had basically seen the questions on the practice tests in the forms of close copies.
Finally, often, people prepare for GMAT verbal by preparing for what the GMAT has done in the past rather than preparing to handle any type of verbal question the GMAT might throw at them on test day. This last issue is quite common since much of what people talk about on forums such as GMAT Club or in GMAT prep materials involves "what the GMAT does," which actually means, "what the GMAT has done in the past."
So, unless you just had an off day, your solution is to prepare for verbal in a way that will result in your being prepared to handle any type of new verbal question you might encounter on the GMAT. To do so, you should work on your fundamental verbal skills, such as skill an analyzing the meanings of sentence versions in SC questions and skill in carefully analyzing the logical relationships between the answer choices and the passages in CR questions. You can use such skills to get any verbal question correct, even a question that does something something different from what past GMAT questions have done.
For some additional insights into how to prepare most effectively for GMAT verbal, you could read this post.
How to Score High on GMAT VerbalAlso, since you're shooting for a rather high GMAT score, you may get some useful ideas from this one.
How to Get a Perfect 800 GMAT Score