You sound similar to me. Social stuff can be hard, it's hard to perceive how others see you etc or how to act in a certain situation. Because of this I tend to be more quiet/reserved as that is safer than trying to be fake, but that's often not well excepted in this extroverted world. I try not to overthink it though. The people that DO know me know I don't mean any harm and as far as I'm concerned that's all that really matters to me.
I often forget about this but I actually am on the autism spectrum, really low though... but that probably does play a bit of a role. But I think it's mostly just the fact that I'm just really introverted, and getting more so as I get older. Like I think back of being a kid in school, and I can't imagine myself going back to such a setting now. Just being constantly with other people all day and not stopping to have to do stuff with them like group projects etc. I just want to sit down in my own work area and do what I have to do.
I consider myself lucky to have a pretty simple job that does not really require any social interactions. I do socialize a lot with coworkers but I also know them well. I'm not traveling to different customers etc like some jobs. I remember when I first started in IT I did get sent out a few times to different customers and always felt awkward and shy. I guess I did something right though as more often than not the customer would actually say good things about me to my boss. So yeah, at the end of the day it's probably best to just not overthink what others might think of you, as it's probably not even bad.
It is true what they say though, as you get older you start caring less and less what people think and I actually see that in myself to some extent.