Thanks for reporting back with outcome. Later, if you want to try it a different way (using automatic syncing), it is often more convenient (depending how often you update songs on the iPod). If your iTunes music library becomes much larger, this may be a better way to manage songs on your iPod.
First, create a new playlist in your iTunes library; you can call it iPod Songs (or whatever you want). From your music library, add all of the songs you want on the iPod to this playlist. You can do this by showing your music library using the Artists or Albums or Genres view, to drag a large set of songs to the playlist at the same time. You can also use the plain Songs list view, and select multiple songs at the same time (such as the songs on an album minus a few songs you don't like).
Then, select the iPod in iTunes to show its settings screen in iTunes window. In the sidebar (along left side), under Settings, click Music. To the right, the iPod's Music settings screen is shown, where you set up automatic syncing.
NOTE: At the time you do this, any songs on the iPod that are not in your iTunes library (on the computer) will be lost. Right now, all songs on the iPod may be in your iTunes library, but when using the Manually manage setting, the iPod's song list is no longer "in sync" with your computer's music library. Over time, there may be songs on the iPod that are no longer in your iTunes library.
On the iPod's Music settings screen, checkmark the box for Sync Music. This turns on automatic syncing. Below that, choose the option to sync Selected playlists, artists, albums, and genres. Below that, under Playlists, find and select (checkmark) that iPod Songs playlist. You don't need to select anything else on this screen. Click Apply to sync your selection to the iPod.
Going forward, to update songs on the iPod, update that iPod Songs playlist in your iTunes library (add/remove songs). The iPod does not need to be connected. The next time you connect the iPod (or click Sync if already connected), iTunes automatically updates the iPod with the same changes. The key advantage... If you ever need to erase (Restore) your iPod due to data corruption, or you get a new iPod (or other Apple device), the iPod Songs playlist exists in your iTunes library. It only takes a few minutes to set up automatic syncing again. It would take hours to manually add the same songs to the iPod, if you can even remember.
I use this method with my iPod nano, except I have several playlists (not just one) that I automatically sync to my iPod, for different purposes. For example, a few of them are for my running. One has my favorite songs, with 5-stars for Rating.