Problems with playing Bluray..

I wanted to play a Blu-ray movie so I bought a Blu-ray drive and a movie.
Then in the player software I get the pop-up that it doesn't support analogue and I need HDMI. I connected my Samsung monitor to the PC via HDMI and started again. I had to switch to "HDMI" instead of "PC" to get to my PC which I thought is fine.
But it wasn't fine. The sides of my screen were cropped and not fit to the screen. I tried to look for help in the options but couldn't find anything and I had my usual 1920x1080 resolution.
The movie DID play but the PC screen just looked bad with a HDMI cable.

Am I supposed to plug in the HDMI cable every time I just want to watch a Blu-ray movie? Can't I fix the screen issues and always use HDMI?