Yeah those stupid wheel collar strip at times.
Or maybe it just slipped. Is there a knotch where the collar with the arm use to be.
You can make a another knotch if you have a drimel.
If not, you can shim it with washers or another coller. Maybe do a little Z bend on the rod if need be.

Or make an arm with a piece of metal and just solder the darn thing on.

Or just use a shorter prop with more pitch
Or use bigger wheels.
Or if you get tired of dealing with darn thing, just go tail dragging