I figured it out. My div takes up 75% of the width of the viewport. That leaves 25% of the viewport width remaining. So 25/2= 12.5. For me to get 12.5% of empty viewport on each side of my div, I need to set either left or right to 12.5%. Not both. I went with the right. Worked perfectly.
#HomeBoxWrapper{
width: 75%;
position:absolute;
bottom:60px;
right:12.5%;
z-index:10;
}