The screen rotations on the final wave of the Boss are the same each time, as follows.

90 degrees counterclockwise
180 degrees
90 degrees clockwise
180 degrees
90 degrees counterclockwise
180 degrees
90 degrees clockwise

Make your move based on where the enemy starts, instead of where it ends up after the screen rotates. For example, during the final Boss' third wave you can use the following moves.

Hit 1: Point down and hit the square using the 180-degree turn.
Hit 2: Point at where the Boss triangle began.
Hit 3: Point at where the Boss triangle began.
Hit 4: Point opposite of where the Boss triangle began.
Hit 5: Point at where the Boss triangle began.
Hit 6: Point at where the Boss triangle began.
Hit 7: Point at where the Boss triangle began.
Hit 8: Point opposite of where the Boss triangle began.