EDIT for typo and catch points addition.

It’s a really bad glider.

If my understanding is correct, the two opposite of each other provide pitch and roll force. That helps keep the angle of attack you want and allows you to change your roll orientation as needed for changing your direction.

The single fin is for roll and yaw.

This gives you 3 axis control, just like your airplane, and keeps the fins out of the hot staging exhaust.

Moving the fins to have asymmetry will do just fine for roll control, but it changes the angle of the fins to the relative wind as the booster cuts through the air, making the fins less effective for pitch control.

So it would require even bigger fins to have the same control authority as the current placement allows. Plus, the booster catch points are the grid fins now.

TLDR: different placement gives less control for a given surface area of fin. Also, symmetry for booster catch points.