My apologies for the delayed response.
You've no doubt moved on to something else by now, but I should still answer your question!
This project was created before I found out about the screen resolution issue you experienced.
If the game is exited while Fullscreen Mode is active, the window will shrink when you launch the game again.
(This issue was fixed in subsequent projects.)
If the Fullscreen Mode option is still visible, turn it off then exit the game. This should reset the game back to it's original size upon relauch.
I apologize that you had to deal with such an issue.