Nero does not recognize the 800M(90 minutes) CD disc automatically. It's still detected as 700M(80minutes) now. 

If you need to burn a full disk of nearly 800M data, you can enable 'OverBurn' feature.

In Nero Burning ROM/Nero Express, open Options dialog. 

Go to tab 'Expert Features'.

Enable CD overburning and set the time to 90 minutes.