It is your interest whether to start preparation for IAS Exam or not. If you strongly want to see yourself as a IAS Officer or an employee of any of the civil services, you can carry on preparation for IAS Exam.
Any way, you have been in preparation for this exam. Soon after the completion of B.Tech, if you speed up your preparation to a little extent, obviously you can crack civil services exam.
In contrast to this, if you have strong interest to pursue your higher studies, you can opt for this course.
The admission for M.Tech course will be given on the basis of performance or score in the GATE Exam.
If you want to join M.Tech, obviously you can prepare this exam. So, no longer you can not continue your preparation for IAS Exam.
So, decide upon yourself of which you want to join. If not interested to join M.Tech, you can opt for other courses like
-MCA
-MBA etc.
My suggestion is to have good prepartion for IAS Exam and crack the exam even if it take 1 more year of time for you to crack the civil services exam. Or otherwise just try for good job opportunities on the basis of your B.Tech academic qualification.