I have great news! I bought 8.5 discs and the project burned. Thank you, all of you, for giving me information and advice to help me finish this project successfully. I learned more about computers and some new terminology from all of you.
When the burn failed, it would have helped if the menu had said the disc was full rather than saying there was not enough memory. Not enough memory made me think the problem was with my computer rather than the disc.
I will say, I did not have immediate success. When I first attempted to burn the project, I immediately got the message "Encoding Title Failure. Reason: E_RPLS_Fatal_Error_Out_Of-Memory Code: 2147766796. I was pretty upset since I had just spent a lot of money on double layer DVDs! I turned my computer off and let it rest a bit and then tried again. The second time the burn was successful. I don't understand why I needed to turn off my computer, but I read that advice in other conversations so I figured it might work.
For other users to know, the burn took longer than usual. I'm not sure if it was because I used a double layer disc or if it is the NXT5 program. It hung up at the same percentage of burn a couple of times and stayed on 99% for over 20 minutes. It was nerve wracking because I kept waiting for the fail message, but it finally finished.
Again, thank you to everyone who replied to my questions and helped me work through the problems with my project. I'm so happy and relieved to have a finished product!