> I taught myself how to code via YouTube
Did you? How do you evaluate the quality of your code? How do you know if there isn't a simpler, more efficient alternative to something you've coded? How do you know if your code is difficult for a collaborator to parse and understand?
In general, it's easy to start "doing stuff" using online materials, but it's very difficult to evaluate the quality of your own work, especially when you're just starting out. This is doubly true in math, where you might be able to develop a half-right intuition that works just well enough to solve a few simple problems, but you have no way of *knowing* whether you actually understand a concept properly without guidance from someone who knows more than you do.