What should I do, take a drop or take the IET Lucknow CSE branch?

It’s difficult to answer this type of question. In any case, you have to weigh a number of things before making a decision.

• If you believe you were unable to put up your best efforts this year but will be able to do so next year, a drop can be a viable alternative.
• If you decide to take a risk, there's a chance you'll end up with a worse result than you have now. During preparation, you'll have awful days, bad mocks, and pressure from friends and relatives, among other things. You'll also have to keep studying while coping with all of this.
• If you've always pictured yourself as an IIT/NIT student, you might want to reconsider. If coding is something you want to do for the next 5–6 years, CSE at IET Lucknow may be able to assist you. But keep in mind that, despite recent advances, placements at IET remain behind those of several NITs and IITs.

To summarise, spend some time analyzing your likely scores for next year and conducting a study into the opportunities you may have. And whatever you choose, stick to it and work as hard as you possibly can.