Excessively Large Video Export Size

I'm currently a high school senior who is trying to make his college music audition pre-screening and I'm running into a video issue on Home Studio 7 xl. When I go to export the file(audio and video) after waiting the 20 minutes to finish the export, the AVI file for a 3:30 video is 31 GB! The file has to uploaded on to youtube, and it's way to large for that. My computer isn't even able to run the video. When I export in a wmv format, the file size is 5.17 MB, but the quality is so bad its also unusable. For some reason when I export as quicktime, the file just completely disappears when it is finished. I'm really not that knowledgeable about Sonar in general, and I really need to get these files down to a smaller size. Any help would be appreciated.