Is a Sacagawea gold dollar coin really made out of gold?

Nope.

The core of a Sacagawea is 100% copper, while the cladding is 88.5% copper, 6% zinc, 3.5% manganese and 2% nickel.

If you think about it for, oh, a second or two, Sacajawea dollars weigh about 8 grams. In the 2010s gold has sold for over $1500 a troy ounce (31.1 gm) so it it were real gold it would be worth nearly $400. Not even the most brain-dead government bureaucrat would authorize minting and distribution of a coin that cost the government 385 times more than its face value.