I need to do a screen recording of the installation process for Ubuntu server and so I installed VirtualBox 6.1 on my Windows 10 laptop. I set up a new Ubuntu VM and booted the server iso file. The display size though is very small, even when I go to Full Screen. I've seen the Guest Additions CD mentioned on a lot of forums, but I get a 'Unable to insert the virtual optical disk C:\Program Files\Oracle\VirtualBox\VBoxGuestAdditions.iso into the machine Ubuntu20' error message when I try, presumably because the server LiveCD installation iso is being used.
I have tried changing the display scaling up to 200%, but this increases the size of the fonts and makes everything look very big and blocky, and is not the look I want.
How can I make the installation of the VM take up the whole of the 1920x1080 laptop screen for the recording?