You can open your video file in DVDShrink using re-author. After you do that you will see on the left hand side a button with 2 arrows. Click it. In there you can use that to set a stopping point in the movie. Make note of where you place it. Burn one half of the movie in this way, then go back and do it again and adjust the slider to burn the second half. It's hard to explain, but once you see it you'll know what I'm talking about.
Or you can also use a dual layer disc and fit it all on one disc.