The solution to every problem I have with my fit and Samsung in general is to throw it away and buy an iPhone. Everything Samsung does is lacking in the user-friendlyness area significantly.
I received a new fit2 pro for Christmas and got the Spotify offline mode working today. Here's how I did it:
1. Set up a Spotify account if you don't have one and then sign up for Premium ($10/mo, first month free). You can do this from your computer or phone, but you can't do it from within the app. You have to be on their website.
2. Download Spotify to your phone and sign in. Set up a playlist you want to use offline (go to Spotify's help section if you need help with that). Make sure your phone is connected to wifi.
3. Click on the playlist and you will see Download at the top with a slider next to it. Move the slider to green and it will start downloading. When a song has downloaded it will have a little green arrow in front of it. When all the songs have downloaded, the playlist title will have a green arrow as well.
4. Open the Samsung Gear Fit app and download Spotify to your Fit2 Pro, if you haven't already. Click on the app on your watch and it will prompt you to sign into your account. IMPORTANT: Make sure your watch and phone are paired, both are on wifi, and both have the Spotify app open.
5. In the Spotify app on your watch, go to 'your music', then 'your playlists'. Click on the one you downloaded on your phone. At the top, you will see the Download slider again. Move it to green and now your watch will download the songs, just like your phone did. Wait until all the songs have their green checks.
6. Still on the watch, click back through the menus and find settings under the Spotify app. Click Offline, and then move the slider next to Go Offline to green. If you go back to your playlists, you'll see the title of the one that's downloaded is green. FINALLY, you're ready to listen to tunes.
A couple of notes: obviously, you need bluetooth headphones paired to your watch to actually hear the music, since the Fit2 Pro doesn't have spreakers. Also, when downloading the playlist, it seemed to go faster (both on the phone and watch) if I clicked on each song, waited for the green check to show up, then clicked on the next, etc. I might just be impatient though.