Q.1After completeing a chapter, you cannot go back and do quests from that chapter?

Is that correct?

Q.2Is the second chapter over after I beat Bevelle Underground temple? cause that's where I am right now.

Thanks for your help!

1. That is almost always true. Very rarely, you can go back and get something, but most of the time, no. However, you can always start New Game Plus after you've played through once. You can even start a New Game Plus in the middle of a playthrough.

2. Yes. And once you're there, I'm pretty sure it's too late to go back.