First of all congrates on qualifiying enterance exams it shows your hard work is in right direction.
As you said you really want to get merit seat and do not want to occupy managment seats then according to me you can take drop for getting merit seat but few things should be kept in mind such as
(1)You will be appearing next year in the enterance exams ,it is a long duration so along with your studies you should keep your confidence high because situations will come when you will need it most . At that time instead of panicing you should keep your confidence high and continue studying.
(2)You will come across many people who will say that you should have not taken drop but remember once you take that decision there is no turning back instead of thinking what they are saying ,you must concentrate on your aim and continue studying.
(3)finally it all depends upon your strong will and desire to get selected in the enterance exam .So always keep them high.
And my sincere suggestion to you is that before taking this decision you should sit back and honestly think what are your strengths and weaknesses related to studies because once you come upon any decision atleast you will be shure that i decided to do this considering all facts and there is no one i should blame for it.
So best of luck and feel free to communicate if you need to know anything else.