Try changing the resolution in the configuration file. It's in this folder located in C:\Users\xxxxx\Documents\My Games\FINAL FANTASY XIV - A Realm Reborn and called FFXIV.cfg

Display setting should look something like this for 1920x1080

<Display Settings>
MainAdapter
ScreenLeft 19
ScreenTop 31
ScreenWidth 1920
ScreenHeight 1080
ScreenMode 2
FullScreenWidth 1920
FullScreenHeight 1080
Refreshrate 60
Fps 1

The screen left and top are what mine is at but i'm using 3840x960 so no idea if the values are correct for you. Screen mode 2 is windowed fullscreen btw.