Take better care of my teeth

Oh god yeah. In my second chance, I'd completely avoid years of Dr Pepper addiction like I did first time around.

Was drinking 4L a day, for months, and didn't realise I had a problem until the day I drank 9L.

realize that my parents don’t care that much about me and get over it

That too.

learn machining from a young age

And that. Woodwork, metalurgy, masonry, etc too. And plumbing and electrics. All the real practical skills.