For me, the most important thing was proving myself that I could do it. Another important lesson was to know my skills limitations (for now, there's alway room to improve) and think of ways to work with them. Keeping the project organized helps a ton when making any change, not only in the code, but also in level, files and assets.
Since I've started learning UE recently, I wanted to make my game on it even with previous experiences with Godot and Unity (but haven't finished any game project till now). Man, it was a ride on learning several features UE5 has, material shaders, post processing shaders or trying out different ways to craft my levels trying to keep it light run.
A phrase that I heard on some videos, "kill your darlings". Learned the meaning in it the hard way, there were lots of interesting ideas in my mind. But there was another lesson, manage the scope of the project. Will it improve the game's experience? Is there enough time to make it happen? Once implemented, where will it be applied? Will it break previous made game sections?
On the level design field, a puzzle in my game has a problem that I later found out. The goal isn't always on player's sight, so the player can solve the puzzle and still feel like is stuck in that puzzle bc isn't seeing the exit.
On the graphics, I learned that keeping a smaller color palette would make my art more consistent as I'm not skilled in the field. But that may not be the case for others.
I would like to apologise to everyone that played my game about the musics. Had to start from 0 to composer in a short time. I mean from zero as I did not even had a clear notion of how the tempo would influence the music.
Lastly, it's okay if the game project isn't the best. Every game had flaws, learn from them to improve.