Not really a problem. I believe the most awesome programmers are the ones that come from a self-taught background. Some employers often see this as a good trait, as you set aside time to learn and not slack off. Also, coming from another field and going into programming is a good bonus as you see programming in a different angle compared to someone who's rooted deep into programming (the "wrote my first BASIC at 4 years old and been programming eversince" kind of person)
> I try to be as full-stack as I can be, but I've tried to focus mostly on JavaScript & Node.js
Don't. You know JS, therefore you know half the story of Node. All you need to compensate for is the knowledge of existing tools and modules. Get another server-side language instead of Node.js. PHP, Java and C# are in the same ballpark in terms of familiarity.
> what can I do to best distinguish myself from the competition?
Just be yourself. That's the best way to make yourself distinguished. Being someone you're not is the absolute worst thing you'd want to show to your potential employer. Show off what you've got, but don't create stuff just to show off. What I mean is, if you have past projects, show them off. Don't create stuff for the sake of that interview. Github commits from 2 weeks ago don't lie.