I'm in the second week of my new masters course and completely understand what you're saying. I'm 44 and got my place based on work experience and professional qualifications rather than having a degree in my subject area. This means there's lots of thing the other students understand better, which is really intimidating.
I've found that trying to focus on why I want to do the course and remembering that I'm there to learn and am not supposed to know it all already really helped.
Try not to overthink things and enjoy the course. Yes it will be hard work, but it wouldn't be worth it if it wasn't