You've got imposter syndrome. Lots of people have it. It's just our brains working against us to exaggerate our sense of inadequacy and then use this to get in the way of doing entirely reasonable and feasible things like reading some books.

For context, to be a socialist means recognizing the falsehoods of liberalism and working against them. Liberalism is hegemonic, though, so that means defenders of liberalism only need to rely on prevailing wisdom and clichés while we inevitably need to know a bunch of stuff to get through to them. Though don't be fooled by that one condescending person! If they were in any way competemt or purposeful about building socialism they would have supported you in joining their way of seeing things, not made you feel like you aren't even a leftist - assuming you weren't saying anything highly reactionary. Anyone that regularly does org work with community recognizes the liberal impulse to dunk on people that don't need dunking on and trains their members to not do that.

I've known lots of people in your boat. The only way I've ever seen them work through it is by building confidence by doing work with an org and by reading the theory that had made them insecure to not know. Not that it was easy. Some did org work and felt insecure for over a year because they didn't dedicate time to reading. But once they did, they felt better and better. I think it helps that other people they felt intimidated by didn't actually know that much, that just reading 3 books put them in a better place to understand theory than the person that made them feel less than. For example, one person's critic was a Trot that wasn't even in an org doing anything and had a series of bad takes that became obvious in hindsight.

Something that helps is by not letting org work or reading be too big of a hurdle. You don't need to run a committee or read Das Kapital right away.

Here is a doable alternative for org work: identify an org by going to an action and asking how you can help. It's okay to dip your toes in. If all you do is support other people in the org by being nice to them and helping out with logistics (taking notes, transporting materials, etc) you will still be very helpful!

Here is a doable alternative for reading theory: read 1 (1) short book over the next few months. Something like Blackshirts and Reads that is written in modern language and is low on jargon. Take some notes on key ideas in each chapter that resonated with you, or just some bullet points.

Okay my comment is getting too long so I'll wrap it up. Don't think of my comment as just saying, "go read theory", because I'm not nagging you or being flippant! I'm still suggesting reading but it is because this is a good way to break through how you are feeling. In this case, you can make the impossible feel possible by doing it in small pieces and at your own pace. And you should also forgive yourself both for your perceived inadequacy (it is valid to feel overwhelmed) and for your reticence. These are common feelings but you don't deserve them. You're already wanting to fight the good fight, there are just some barriers, and, like most people, one of them is your own brain!

Please feel free to PM me if you prefer that, I have worked with and mentored many people in your boat. Replying (or not) here is also totally cool.