Trouble installing the turn signal arm

Hello. I'M having a problem with a new signal part. As the photo shows it doesn't go all the way down. Has anyone had this problem. If so what did you do to fix it.
Thank you in advance.
Ted

View attachment 1715588181
I have not had this problem but are you running out of threads on the screw? Or is it the slot in the the switch that's to skinny? First thing I would do is compare the slot end of the new switch to the old one.