I am wondering if anyone could help me and tell me how they get a perfect 90 degree angle on cake once they have put their fondant on it? Mine always seem to be rounded not a whole lot but not that perfect 90 degree.

its mostly the nature of fondant, the weight of it will drag its own self down and end up rounded. its all in getting your cream underneath crisp, i find it much easier with ganache to get crisp edges, if you can make that nice and clean and sharp, your fondant will be, and use two smoothers, one on the sides, and one on the top, makes the world of difference.