@LoricGarde: Thanks for letting me know, I'll look into it later today and release a fix, no worries ^__^
It's also possible to resize the window manually to the correct size and aspect ratio.
Update: Alright, uploaded a new version with a higher starting resolution and the fullscreen mode isn't a blurry mess anymore.
If your windowed screen is too tiny/big, just resize the window as you see fit.