Ah, that's unfortunate. Usually you should be able to go fullscreen by selecting it in the popup window where you choose the resolution--does this not show up at all on Linux? (The Linux version wasn't properly playtested, sorry about that.)
Ah, of course. I played it on PC too and I remember there being that popup. That window doesn't show up in Linux though!
Hope you find the time to fix it, if not then I know how it is :)