m.2 adapter board screw missing?

[tophneal]

You're not missing a screw. The brass stand off is used to retain the nvme drive in place. The indentation going around the brass standoff should be closer to one side than the other, that side goes up when looking at the board. The notch of the drive will fit into that indentation. This photo should give you a good idea how everything should be installed: https://forum.pine64.org/attachment.php?aid=1672