The core mechanic in this is really inventive! I loved the 3d pixel art aesthetic you went for and the variety of mechanics that discourage both having an extremely wide raft and a width 1 raft. That said having a narrow raft seemed in general like a pretty good strategy and I was able to get 353m with it.
One thought I had was since the game is in 3d and you can jump it would be really cool to have obstacles along the z-axis (or y-axis depending on how you implemented this :p). Jumping only seemed useful for crossing 1 square wide gaps in my raft but I could easily imagine stacking blocks to build a raft of greater height to collect some power up above me (stacking blocks right now seems to just overlay them on the same square). Or maybe there's a log that fell down horizontally across the entire river and your raft is able to pass under it but you need to jump over it to avoid falling into the water.
Anyways, great game and definitely deserving of its popularity!