First time with M2.
 
I followed book and no matter what I do this screw sits like this. Should I be concerned? Should I just loosen the screw so it sits level and leave it?
 

 

....or try it without a washer

I had the exact same thing happen -( with the exact same M.2 card) -though I may have cross threaded but more tries the same.
I posted in another thread that side forces my be my problem with my Samsung M.2
 
System worked fine.
 
I think the confusion about a washer is in the picture the top of the MB mounting post striated ? 
 
Next person may want to check M.2 board length   _ I did not have this problem on the two M.2 in the Z270 chassified K
using Intel and crucial M.2

It's been 24 hours and no issues--I do like the 2 second boot up :D