Other people will be reading it and making critiques, and they'll especially hate it if I write people ooc or forget important lore. So, yeah. Don't know what to do.
Nowadays (at least in my experience), fanfic critique is not something that seriously happens in the open (by that I mean the comment section on the site it's posted), mainly for the fact that people know it's not something to do unless asked to + serious critique is hard to come by because most people active right now in newer fandoms are quite young and don't know how to properly write a critique without it being "I didn't like this because it doesn't suit my taste therefore it sucks". So I would say that you most likely won't experience that, even if the fandom is on the older side, since people do tend to look for 'critique wanted' when doing so. In general, they're left for private servers or beta readers if you have one.
Additionally, most strict in character people and lore enthusiasts don't particularly go into the fanfic sphere as much as other fandom goers, so I doubt you'd encounter them in the wild. People aren't as strict with canon as it might seem at times; fanfic is there for the person to write whatever they want, even if it goes against canon information.
I don't think you should be too scared of trying fanfic, since at the end of the day, it is for you, even if it might not seem like that at first glance. It can be hard when you don't know what to do or what direction to take but it all evens out after a while.