You can cut a 48" wide panel with the 55" rail. Suggest you overlap toward the start of the cut so that both green guides on the saw are engaged on the rail. That should give you enough distance to get through the cut and just run off the end of the piece.
Ideally, you'd have a few more inches on the rail beyond the 55", but it will cut 48" in my experience.
Ideally, you'd have a few more inches on the rail beyond the 55", but it will cut 48" in my experience.