WhiteHandAre there no other keycaps included with your board? You need a 1.25u-sized Fn-key there, but that 1u might have been included for people that put it to the right of the r_Shift key (where PgDn is currently on your board).
But, they also could have just sent you the wrong keycap, seeing as they're giving you incomplete keycap sets with only enough keys to fit these "Premium", "Signature Series" keyboards...