Ginny is rather more than six months younger than Ron: you obviously need to check on where you got your "gestation period" from, because it's way out.
Ron was born in March 1980, Ginny in August 1981, making her roughly 17 months younger.
Oh, and I agree: take the song out, it just gets in the way.
Obviously you didn't read the summary. I said that the story doesn't follow cannon.