Yes, TOPPING is a Scrabble word!

Letter values in Scrabble US: T 1, O 1, P 3, P 3, I 1, N 1, G 2.

Is it a valid word?

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

be superior or better than some standard
pass by, over, or under without making contact
be at the top of or constitute the top or highest point
be ahead of others; be the first
provide with a top or finish the top (of a structure)
reach or ascend the top of
strike (the top part of a ball in golf, baseball, or pool) giving it a forward spin
cut the top off
be the culminating event
finish up or conclude

Also: go past, top out, top off, top-flight, top-hole.