IMDb primarily records on-screen credits. If you were credited on screen as "Extra", you may certainly add yourself, although you may need to supply evidence such as a screencap of your name in the credit roll.
IMDb does list some jobs where the person was not listed on screen with the
(uncredited) attribute, but only if that person already has an IMDb listing for a job where they were credited on screen. Also for cast that person must be visible and clearly identifiable on screen, not just in a crowd, or a fleeting glimpse.
See
I appeared in a film but my name is not in the credits. Can I be added to IMDb? for the official word on this.
If you give the details of your appearance in a reply here, someone here may be able to give you more specific advice.
