If your inventory is already full you wont be able to pick anything up you can always press "Q" to open it.
Okay, I did re-test the game. And found first small fishes I was able to catch. Maybe add a little notification "fish caught" or "nothing caught" so there is some feedback as to what I caught every time player finishes reeling in (same notice as "Fish too heavy").
And I still have problem with "Follow player" turning off whenever I use sonar view. I would recommend to keep "follow player allways on, and showing sonar view around mouse cursor, not just around viewport center.