My wife is việt, she told me to say. "Anh là qủa em”. She says "bạn it's sorta like 'you' but literally translates to friend. Tôi is also an uppity term when referring to yourself when you're talking to peers"
I speak Việt, but learned from my houshold, and this sounds a little off to me. It doesn't sound right in the context of: I am yours. It does sound nice when spoken in English, but in Việt, this is just no. Maybe it is too cheesy.