I don't think books and tutorials help that much. Playing and making games — a lot of games — might help you grow more as a designer than reading and watching YouTube.
1. Do master studies. Take a tiny environment or mechanic of a game you love and reproduce it for education, knowing you'll throw it away. Do this often. Get faster at it.
2. Ask people what their favourite game is. Play it. If it's fun to you, why? If it doesn't resonate with you, why?
3. Internalise the idea that ideas don't matter that much, execution is what matters. Good game designers can make otherwise boring games feel fun to play. (See "the art of screenshake" below.)
4. Make a lot of games. Make them small enough to finish. You don't have to release them all, but you should watch other people play them sometimes.
5. Don't listen to people who tell you not to watch YouTube for game design ideas, there are plenty of great videos out there that have positively changed how I think about game design:
The art of screenshake (starts a little slow, but stick with it!):
+1 for make a lot of small games you can finish. Game jams / hackathons are good for this [1][2]. The fact that OP got their demo in front of people in ~6 weeks is heartening though for that aspect, many people lock themselves away for years only to discover their efforts were ill-advised.
1. Do master studies. Take a tiny environment or mechanic of a game you love and reproduce it for education, knowing you'll throw it away. Do this often. Get faster at it.
2. Ask people what their favourite game is. Play it. If it's fun to you, why? If it doesn't resonate with you, why?
3. Internalise the idea that ideas don't matter that much, execution is what matters. Good game designers can make otherwise boring games feel fun to play. (See "the art of screenshake" below.)
4. Make a lot of games. Make them small enough to finish. You don't have to release them all, but you should watch other people play them sometimes.
5. Don't listen to people who tell you not to watch YouTube for game design ideas, there are plenty of great videos out there that have positively changed how I think about game design:
The art of screenshake (starts a little slow, but stick with it!):
https://www.youtube.com/watch?v=AJdEqssNZ-U
Designing to reveal the nature of the universe:
https://www.youtube.com/watch?v=OGSeLSmOALU
Game design is a search algorithm:
https://www.youtube.com/watch?v=o5K0uqhxgsE