When it activates, it will only count for that shot.
Don't mix it with your entire "turn".
A shot does not necessary mean a turn.
Sometimes, a turn can have 2 shots or 3 shots or even 5 shots.
Example with PowerUp 1 (The red arrow; the one that gives you two additional shots, a total of 3 shots)
1) First shot, normal damage.
2) Pearl activates!
3) Second shot, 200 points to offense -> A bit higher damage.
4) Third shot, normal damage.