How many grams of water are formed when 43.4 g of hydrogen are consumed in an excess of oxygen?

I got 390.6 is this correct?

Probably. I obtained a slightly different value but we may not have used the same set of numbers.

43.4/2.016 = 21.53
21.53 x 18.015 = 387.8 which I would round to 388 to three significant figures.