Sounds like you just chose the wrong disktype. Nero can burn Dual layer disks as well and if you chose that then it will just stay inside 8.5GB instead of 4.38 like we want.

On the first screen in Nero Vision where you import the files, you can choose how big the disk is (it should say DVD, and after importing the file(s) it should say x.xxGB of 4.38GB used. You can go over the limit because when you choose fit to disk, Nero will do just that.