Avid DVD (Sonic DVDit) does not export .iso's at the correct size

Hi, I've been using Avid DVD (Sonic DVDit) for a while and had no problems at all with it until now. Yesterday I created an .iso through Avid DVD and it said that I had 100+MB of space left on a 4.7GB DVD. Once I went through the 3 hour long process of transcoding at high quality - It turns out it is a 5.2GB image file. I thought maybe turning off OpenDVD and trying again would do the trick (never had problems with that before anyway) - 3 hours later, the same problem. I looked in the project settings and it said that the project size was like 5+ GB and the size on disc was 4.57GB or something like that. I assume the huge project size is due to the fact that I created the .iso in the same folder as the project. I created a whole new project and started from scratch, still the same thing. I even recreated my quicktime reference files with Xpro. I don't know how much quality loss will be if switched to low quality. I have created .iso's with the same lenth of video and the quality settings... Any help is appreciated!