There are many ways you can do with the locked and unlocked screen. Of course, it takes some time to get used and I remember that I used to struggle with it back then. However, I found a way that makes everything easier for me.
Try this:
Go to the "HOTKEYS" tab and find the "Camera Control" option.
In the "Toggle Camera Lock" section, bind that option to the SPACE bar.
After you have done that, you can lock and unlock the camera by pressing the space bar once at anytime. It will take a bit to get used to, but this is what feels comfortable for me. I feel uncomfortable if I hold down the SPACE bar the whole time while fighting, so I use that option instead. I lock the camera whenever I'm fighting in a certain area and unlock the camera whenever I need to look elsewhere on the map.
Play a few Co-op vs AI games and force yourself to learn the lock/unlock camera during the game. Then, move on to normals and you will get used to it eventually. It just takes time.