Hi,
I know this post is a year old, but I stumbled across it while looking for answers to this problem. I eventually managed to solve it by making my main content div 100% width to allow for the fullwidth modules, and adding the following code to narrow the standard width modules:
.et_pb_row {
position: relative;;
width: 75% !important;
max-width: 75%;
margin-left:auto;
margin-right:auto;
}
You can set the width to whatever you want.