All photos lost quality.

I just finished making a 2 minute movie in Movie Maker. It is simply 2 minutes of music with 93 photos scrolling through as a slide show.  The pictures look great small in the creation screen, but when I make it large screen, they all look pixelated.  And they were not always looking like that.  As I was creating the movie, I was periodically viewing it large screen, and it was looking fine.  It wasn't until I neared the completion of the movie that they all became distorted.  Please help!  This is for a presentation to hundreds of people tomorrow night!