Yes, TOTALLY is a Scrabble word!

Letter values in Scrabble US: T 1, O 1, T 1, A 1, L 1, L 1, Y 4.

Is it a valid word?

TOTALLY is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

to a complete degree or to the full or entire extent (`whole' is often used informally for `wholly')