Yes, FINBACK is a Scrabble word!

Letter values in Scrabble US: F 4, I 1, N 1, B 3, A 1, C 3, K 5.

Is it a valid word?

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

large flat-headed whalebone whale having deep furrows along the throat; of Atlantic and Pacific

Also: finback whale, fin whale, common rorqual, balaenoptera physalus.