I tested our live preview and as you said it’s looking good on retina screen (MacBook Pro).
I really can’t help you without seeing the website. I can only assume that problem is with CSS for some reason but if rest of website is sharp that means that script for retina images is working fine.
You can check for example Search icon (with magnifying glass) CSS. Background image that must be loaded has suffix “2x” like below:
background: url('../email@example.com') no-repeat.
In case that retina images are not loaded, image will be without “2x”;
background: url('../img/search.png') no-repeat.