I think you might be taking the wrong perspective on this. Everything is a learning experience, even an interview where you didn't get the job. You didn't know what a join table was, now you do. Doing a bit of research on typical programming questions would probably go along way to close the gap. You can go back to your existing projects and rewrite them with a join table, and with a little research you could probably get the app in a better state that you will look more attractive to a prospective employer.

You obviously learned a lot while building these side projects. I've certainly done things on my own without knowing the proper way to do it, only to learn there right way later on. You clearly know how to write code and build stuff. Being an EE major you understand logic. I don't think it would be too difficult to make the transition to developer.

How many interviews did you go on? I'm employed and when I was looking for a new job I had some stumbles. This is part of life. Even with the gap between supply and demand for programmers , some employers are going to be picky in what they are looking for.