Not pursuing my singing career when I was young enough to really do it.
3. Getting my degree in English instead of theatre or vocal performance.
Nothing you can do about the degree (unless ya go back for it), but you can ALWAYS better yourself artistically, especially if you love it. I mean, i've given lessons to people who are grandparents, they just want to learn. That's what's amazing about the human mind, we can always learn. There's really no excuse to pursue singing if that's really what ya want to do.
Hell, I'm behind ya!
