I've found that the best way to learn how to pick small enough ideas for a game jam is to just keep doing jams. It doesn't have to be perfect, it doesn't even have to be complete or playable! The important part is to try, to gain experience, and to learn how you work and where you tend to stray off into the weeds. I'd really encourage you to keep trying! What you've done so far is great!
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Again thank you for your kind words,
Loved that you enjoyed the game.
I will probably do these types of jams again but I definitely need more experience in a tense environment like Jams first. This is my third GameJam and all of them have been equally hard, the first Jam I did I still haven't touched unity yet. I'm simply more used to a more lax schedule. I will keep doing Jams in the future don't worry, it's simply that 3 hour ones might be too soon for me atm. ^^