Downloaded playlist not adding new songs

[J805]

I have downloaded one playlist of 128 songs on my Samsung Galaxy J7 which I have a 64gb SD card installed on. It downloaded fine, then I went back to my computer and added a few more songs to this playlist but my phone will not downloaded the new songs I added to it. It still shows 128 songs while my computer shows 132 songs. I have plenty of space on my phone and have confirmed that I am storing spotify data on the SD card. I tried logging out of the app, and also rebooting the phone. I don't have to redownload the whole entire playlist again each time I make changes do I? This would be a terrible waste of bandwidth if so.

What am I doing wrong?