If trying to make an audio CD from MP3 tracks that WERE continuous, there will normally be a slight gap - if there's a 2 second gap, ensure that you are using DAO mode, and that you turn off or zero 2 second gaps if added by software.
The only way to cover the joins, is to use a small amount of crossfade - VERY small. Play/preview the join and use the minimum required to cover it - a few frames ought to be enough.
Nero FULL or DEMO, but not OEM or BUNDLE, supports crossfade.
If you have a bundle or OEM version, find and save the key from the registry, then deinstall it and load the current demo version - after doing the task in Demo mode, apply the saved key to convert to licenced bundle/oem version.