should I take CS as a side subject with PCM if I don't want to do engineering
Hello!
You can take Computer Science along with PCM if you are interested in the subject. Even if you don't want to pursue engineering, studying computer science will not affect anything. Rather it will help you understand more about computers, software and systems of computer which is necessary in this digital age.
If you're interested in the subject, you can also pursue your bachelor's degree in Computer Science or IT.
Hope this will help you.