Any QUICK advice? Moving back to USA... tomorrow

Even now, if your Cdn passport has expired, you are under nio obligation to return it with your passport application.

Only current unexpired passports need to be submitted for cancellation.

A Cdn passport is invalid after it has expired. nothing to be done to it.

And, yes, given your dual status, it would be useful to mention Cdn passport and American birth cert, etc.

Citizenship by birth implies citizenship bestowed at the time of birth, rather than by natuarilation or (in csome countries) by marriage.

So, no, US by birth does not mean born in US.