I think tuning the difficulty is the hardest thing to do during a game jam. When I did the first VIMJAM a couple years ago, I got a lot of comments saying my game was too difficult which I didn't think so while testing it because I had played the game 1,000 times before uploading it. Also the full screen thing is kinda just preference I think if you decide to take the game further, you can always start the game full screen but give the player the option for windowed/fullscreen