Composition too small for trapcode effect but increasing the compositoin size ruins trapcode effect

So I created a 400x400 comp with three Trapcode effects: Particular, Shine, & Lux. Lux is causing some glow spill off the edge of my canvas so I would like to increase my composition size.

However when I change the comp to 500x500 I get a weird crop where I only see part of my original canvas. If I try to change it to 1000x1000 then I cannot see any of my work.

I realize that this is inherently silly because I made my comp too small to start with, but I'm wondering why I can't make it larger. I've run into similar problems in Photoshop but I can always expand my canvas.

Thank you in advance for any advice on the subject.

-E
-vimeo.com/36013051 (reel)
-RambozMediaGroup.com (production house)