How make this GUI box aspect ratio thing?

I’m working on a new Game that involves cutscenes and animation like Konethorix’s.

I don’t want players to have a wide view since it gives them view of things that aren’t
supposed to be seen.

Do you mean something like this?

You need to be careful about setting your Scale since it’s going to be different for different devices aspect ratios.

This is probably what you’re looking for: