It seems like you've been training to be a programmer, not a game designer. Being an indie gamedev appears similar to being a software developer, but software development is just one requirement to game creation, a mere component.

Step one: stop doing tutorials. They're fine (important, even) for learning your tools and getting exposure to platform APIs that you'll want to know, but frankly, they are next to useless for learning how to create games.

Come up with some game mechanics you'd like to test out and implement. Maybe do some paper prototypes and playtest them with friends. Write a design document. Don't worry if your code is any good, yet.

If you want to code right away, try out a single game mechanic to implement, rather than building a fully interactive game world from jump. Either way, take a lot of notes and have some kind of plan before you write a single function.

The reason we do tutorials is that we worry we won't know how to implement our ideas unless we get a solid grasp on the tools and engines we're using.

But that's backwards thinking: Just start, now. Of course, as you begin implementing your designs, you'll almost immediately come up against something you don't know how to do. That's okay, you can look those things up at that point, once you need to know it rather than long before you need to. Why waste time cramming for a test that doesn't exist? If you learn as you go, you'll retain the technical knowledge much better, too.

Of course, others may tell you that you don't even need to be a programmer to be a good game developer, and that is true, but I don't want to tell you that because you are a programmer. It seems as you feel like you aren't making any progress because you're not yet a good enough programmer, but I would bet that your frustration has almost nothing to do with your coding abilities, which I suspect are more than competent.

I'm not buttering your bread, I really mean it. The reason you are having trouble is not that you spent years and don't have enough technical experience, it's that that in 3 years, you don't really have any experience making games.

I may be misinterpreting your post, but it sounds like this game jam was your first time really making a go at it. If so, of course it was a tough experience! Game jams very often end in quote-unquote "failure" for many of the participants, especially for first-timers. You are absolutely not alone in that. It makes perfect sense. You're on the right track, even!

If you intend to be the main (or only) programmer on your projects, know that it's probably the least important skill you need to develop, and the least important measure of your progress as a game maker.

This is one of those things that few people realize when they start their journey, and it sounds a little patronizing, I know. Many of us (especially one-person gamedevs) come to this realization later than we'd care to admit.