https://www.folkd.com/submit/ukeuniverse.co.uk//
That's because the chords you're playing are in one key and the song was recorded/written in another. Why? Because oftentimes, the chords you find in fake books, song sheets and online sites are transposed into a key that's easy for beginners, like the key of C. The chord progression is the same but the key is different. That's why it sounds fine when you're singing and playing the song by yourself but not fine when you play along with the recorded version. Listen to lots of ukulele players. The more you listen, the more you'll get a fee