problems fitting bee sting aerial to W168

[faulkner9]

hey, having a few problems fitting this to my A class w168, the bee sting aerial unit is being stopped from going on by a metal unit underneath the aerial which had a screw inside (which i removed), where i gather the screw provided in the pack goes, but the screw isnt long enough and the aerial doesn't sit right. Do you know if i have to take this metal bit off somehow or do something different?

cheers for any help!