Can you change game window size in ScummVM like you could in Dosbox by changing resolution in config files (like making it twice as large) ?

You can change the window size. I'm sure there's some way by doing it by adding something to the config file (queen.ini). But there's also another way:

Right-click on the "Flight of the Amazon Queen"-icon and choose "properties". You will see following line:
"C:\Games\Flight of the Amazon Queen\ScummVM\scummvm.exe" -c "C:\Games\Flight of the Amazon Queen\queen.ini" queen
Insert -g2x (for double size) or -g3x (for triple size) before the last "queen".

For example:
"C:\Games\Flight of the Amazon Queen\ScummVM\scummvm.exe" -c "C:\Games\Flight of the Amazon Queen\queen.ini" -g3x queen

Does that help?

I will answer when I return home from work and try it :D
Thank you for help.

You're welcome!
But that's weird... x3 should give you a bigger window, than x2 does. There's also 1x, but nothing above (x4, x5...) as far as I know.
Are you running Windows or a Mac?

I'm running Windows.
I didn't say there are something above x2 and x3, just this 2 options, but I dodn't see program respond really to them. But I could just didn't compare it well. I will not test it right now as the game looks fine as it is. Maybe when I finish it I will experiment.

You can use: Ctrl+F5 -> Return to Launcher -> Options... -> select a graphics mode -> OK -> Start
Personally I use the HQ3x mode, it looks best on my system.

Any idea how to do change the window size on Mac?

EDIT: Nevermind, I found it!