OK…AFAIK, although ST2 can handle SASS/SCSS (because at the end of it all it’s just a text-editor) it won’t automagically parse and create a CSS file from your SCSS file. You have to use an app.
I’ve started using Prepros (http://alphapixels.com/prepros/) and it’s the bees knees.
Create a blank file and name it with a `.scss` extension. When Prepros goes to work it automatically creates a CSS file for you.