I'm on the right edge! (3)
I believe the answer is:
rim
'edge' is the definition.
(rim is a kind of edge)
'i'm on the right' is the wordplay.
'i'm' becomes 'im' ().
'on' says to put letters next to each other.
'the right' becomes 'r' (common abbreviation).
'im' after 'r' is 'RIM'.
(Other definitions for rim that I've seen before include "Edge, border" , "Brim, edge" , "Curved edge" , "Circumference" , "Upper or outer edge" .)