Hi, Can you see where I have gone wrong with this please?

Question: Simplify $\displaystyle (x+x+2x^2)^3$

$\displaystyle (x+x+2x^2)^3$

$\displaystyle =(4x^2)^3$

$\displaystyle =(4)^3\times(x^2)^3$

$\displaystyle =64x^6$

(The book's answer is $\displaystyle 27x^6$)