Yes, BAGATELLE is a Scrabble word!

Letter values in Scrabble US: B 3, A 1, G 2, A 1, T 1, E 1, L 1, L 1, E 1.

Is it a valid word?

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

a light piece of music for piano
something of little value or significance
a table game in which short cues are used to knock balls into holes that are guarded by wooden pegs; penalties are incurred if the pegs are knocked over

Also: bar billiards.