A boat never travels where its bow points. It travels along the resultant — the vector sum of its own heading through the water and the river's current.
Point the bow straight at the dock and the current adds a sideways shove the whole way over, so you land far downstream. Aim the bow upstream instead — the "crab angle" — and the current's push exactly cancels your upstream lean. The resultant then points dead at the dock and the wake runs straight.
The dot product vₓ·vₐ measures how much of your effort lies along the current. Aim straight across and it reads zero — none of your push opposes the drift, so the river steals the entire crossing.
Bush pilots do exactly this in a crosswind, and navigators did it by hand for centuries: the same triangle of velocities lands a plane on the centreline and a ferry at its dock.
Something in the simulation stopped unexpectedly — the lesson continues without it. Nothing you did was wrong; you can move on.