You do stick your butt out with squats. It's not a plie. You just have to do it exactly right or you hurt yourself. And there's nothing wrong with doing squats with something under your heels. I can't remember what we used in my weight training class, but I swear there was something (though I could just be delusional).

The bar weighs 45 pounds. Unless you have at your gym something that isn't the standard weight bar.