I can only think of 2 scenarios here, as I don't know which applies I will answer both
You are working on a partial and it then, upon save, compiles all of your CSS files
I'm afraid that this is at the core of its design. I have an open issue on my updated, and still maintained, version of this extension (also available on the VS Code marketplace here)
You only want one file to be watched and processed
You must change some settings to watch only that file
how can i watch only the file i'm working on? right now, it watches ALL the scss files