Imax1 said..
First make sure the fin head is not too deep. Zooming in on the pic ,I notice the back end of the base is round with some file marks. It should be square with rounded corners. Has someone previously built up the head and badly fitted it into an oversized box ? I would start with filing the rounded point of the head to match the square profile of the box. Slowly , slowly, little by little using the screws.
That’s how it came from the factory
