So I intend to do it in both shell and disk ways.
Let's first use shell method (formula: $\int 2\pi x(f(x)-g(x))dx$):
Since $x=3$ is the major axis, and $y=(1-\sqrt{x})^2$, we have $V=\int_0^1 2\pi (3-x)((1-\sqrt{x})^2)dx$
Next, disk method (formula: $\int \pi (f^2(x)-g^2(x))dx)$: we have $x=(1-\sqrt{y})^2$$V=\int_0^1 \pi ((3-0)^2-(3-(1-\sqrt{y})^2))dy$
Did I write my equations wrong?