any tips and tricks for getting music to sync to Apple watch SE in a timely manner?

Hi,
I recently got an apple watch SE2, and I think I'm going to like it. But why is it such a pain to get locally stored music onto it? I have a set of 4000 songs, which take up about 3 gb, so not very big, that I insist must be on my apple watch. Why does it take seemingly forever to get them synced from the iPhone onto the apple watch. If I'm lucky, some will sync, but then it gives the message "downloading will resume when apple watch is charging and connected to wi-fi. Duh, the apple watch is on the charger, I haven't moved it, it's also connected to wi-fi. How can I get rid of that message and force the sync process to continue? You might ask why I don't just stream apple music. I like my music offline, and also a good majority of the stuff I have is either homemade, or it's so rare that it's not available on apple music.
I could probably airplay music from my iPhone to my apple watch, but that would defeat the purpose, I really wanted to be able to go work out on the treadmill on the other side of the house and not have to take my iPhone.