Since I discovered that I need an empty spool anyway, I've decided to use this roll as a practice roll, so I've unrolled the entire roll to see how the other end looks like.
I've also practiced attaching it back to the spool and rolling it back.

Since the film is intentionally ruined now, I'll use its spool as the starting spool (you only need one empty spool in your lifetime for starting MF photography)