The basic issue: the video preview looks perfect in Vegas, but after rendering, the background image extends beyond the output aspect.

I'm putting a cropped image over a background track that I'm expanding the width of the window and applying a gaussian blur. The project is using NTSC DV 720x480 (lots of old footage, so I chose to make the whole project match it). I've done 'match output aspect' on this background - it looks great in Vegas but it still stretches beyond 720x480 in the render. It's not a huge difference but it's still distracting.

I know I'm missing something, and hope you can spot it in the following photos (I'm not sure how to paste a photo here, so I'm sharing links)!

Here's the preview

Here's the render - the blurred background is about 2x too big on each side of the original photo

Here's the Video Event FX window with settings

Here's the Project Properties window

And here's the Render Settings window

Thanks in advance!