Welcome to imposter syndrome, it means you're a professional.

As far as how you can be more comfortable that heavily depends heavily on what your job is. Some jobs have more direct feedback than others. But largely it will just take time. You're still the new guy from the sound of it so it will take time to learn how your workplace works and what the exact expectations are. In the mean time just remember that as long as you aren't consistently getting negative feedback on the same things then odds are you're doing perfectly fine. Doing things wrong ocasionally is expected because you are human, but as long as you are learning from those times then you are already doing better than a lot of people. If nobody is telling you that you aren't meeting expectations at your reviews then either you are meeting expectations or you have a bad manager.