Try putting it in fullscreen and clicking apply. Then go back and change the resolution.
If that doesn't work:
- In your Blockland folder (found in your Documents), go to "config/client"
- Open the file called "prefs.cs" in Notepad.
- Add this to the end of the file:
$Pref::Video::fullScreen = "1";
$Pref::Video::resolution = "1366 768 32 60";