Making a mistake bedding American stud? (7)
I believe the answer is:
earring
'stud?' is the definition.
(stud is a type of earring)
'making a mistake bedding american' is the wordplay.
'making a mistake' becomes 'erring' ('err' can be a synonym of 'make a mistake').
'bedding' indicates putting letters inside.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'erring' going around 'a' is 'EARRING'.
(Other definitions for earring that I've seen before include "Stud, perhaps, or a drop?" , "Ornament on lobe" , "Aural pendant" , "Piece of jewellery" , "Otic adornment" .)