should i retake these SAT II's?

<p>in may this year i took the US History SAT II and the Biology (Molecular) SAT II.
US History: 680
Biology M: 720</p>

<p>i am wondering if these should be retaken. i am planning to major in biology/animal science/zoology and my current goal for college is Berkeley or Stanford, reaching for Harvard.
i am assuming that i probably should retake biology, sinc ei'm majroing in it, but i'm not sure how much my history score will hurt me.
is world history an easier test than us history?
btw, these tests were taken after less than a week of studying. i am hoping that if i study more over the summer i should be able to get 750+ on both. i am also planning to take Math IIC and maybe Lit or World History.
thanks for your input!</p>