How do I upload the music on the watch?
1. The music is not DRM protected
2. The 'Share iTunes Library XML with other applications is set
3. If using iTunes on a Windows PC then then it maybe an issue with the current MySports Connect and certain versions of iTunes under certain conditions. Apple changed the name of the library from 'iTunes Music Library.xml' to 'iTunes Library.xml'. This should be fine since MySports Connect uses the preferences file to get the library name. However Apple made another change and there is some situation where the preferences file does not contain the name of the library xml, only the .itl file. In that scenario MySports Connect can not find the .xml and therefore shows no playlists (the 3.1.3 or greater version of MySports Connect with fix this).
So if you only have a 'iTunes Library.xml' you could try copying it to 'iTunes Music Library.xml' and see if MySports Connect can then find your playlists. You would of course need to copy the file if you added new playlists that you wanted to copy to your watch.