I cannot figure out what I'm doing wrong, my weight is off. I don't see where my mistake is at...
I look at you model and looks like you have some missing dimensions. I assume that R45 you made it tangent with side walls and bottom. maybe is tangent with vertical A dimension and that will change you part mass. Maybe is not tangent and that will change again your part mass... Plus A dimension is not really clear.
Try to draw first all exterior walls connected with A and B dimensions and after that add 45radius, with radius feature.
The Dia. A dimension is incorrect. It needs to refer to the virtual intersection of the angled side wall and the horizontal bottom wall instead of the bottom radii tangent point.
Its easy to create a point at his virtual intersection, just ctrl select the 2 lines and create a sketch point. The system will place the point at the virtual intersection.