Hi EmilsVFX,
It’s all there 
What you search can be found in the Properties Sidebar. Open the View tab. Expand the lock subtab. And here untick Lock Camera to View. And when done, tick Lock Camera to view again so that you can go on with the usual navigation in camera view.
There is another way too, that fits the camera view in width into the current view. It’s in the View menu. The menu point View Camera Center.
Hope that helps
Kind regards
Reiner