I am in 11th.I am aiming for IITB with CS and have wasted six months . Should I take a drop?

You are in XI or XII.

1. Timing and time both are important in JEE.You need compounding to work in your favor.Minimum preparation time for JEE is 5 months if the basics are all clear.
2. You need to make notes, revise weekly and solve atleast 30 problems per day per subject.This amounts to at least 10 hrs per day of self study.
3. If you know you can do well in future with hard work , only then consider a drop.