I never really knew imposter syndrome until I started working for myself. Interestingly a lot of the artists I follow mention dealing with this. Most of the time I try to ignore the thoughts that I'm not legit or that I don't know what I'm doing. They're easier to ignore when I can have fun with a project because having fun doesn't necessarily rely on experience. And usually the end result is better when having fun no matter how legit you might be.