trouble installing fin

Hi im brand new to SUP. I just bought a board and fin off of someone and I am trying to put the fin on the board. The board is a Tahoe Bliss and the fin is also a Tahoe fin. I can get the back part of the fin into the square wide opening but it will not slide back either direction into the channel. However if i turn the fin around so that its facing the wrong direction then it will slide either way into the channel. Obviously that won’t work! I notice on the fin that the screw is much longer on one end than the other. Is this normal? Am i doing something wrong? Did i buy a defective board or a defective fin? Here is a picture of the back of the fin metal part thing:

Appreciate any help!

I had same issue
With my Tahoe Bliss. My hubby shaved off a bit of the part that slides into the track. Works fine now.