Why are there 2 versions of Bella's lullaby??

Correct, only 1 version. Before the movie came out, YouTubers adopted River Flows in You as what they thought Bella's Lullaby should sound like, and that is now what it's widely known as. The version from the movie was composed for the movie, and is the actual Bella's Lullaby, though Yiruma's song may be more fitting.