Is HER-2+++ always aggresive?

I was given the statistics by my onc that i had 70-80 chance of never having the big C again after being treated for early BC(stage 2b with 3 nodes involved) I then think I challenged him on those staistics when i found out my HER-2 status. He lead me to believe it didn't make much difference. I read this site a lot and all you women are fabulous but I am still left wondering if it will DEFINITELY be me in X number of years. And then all the drama of changing diet and not eating sugar(as I eat my Toblerone)I think is it worth it if it isn't going to make much difference?
Confused