It should be like Marcus says: under the "Expired Ads" header in My Pinside > Ads. Are you not getting those buttons for some reason? Or is your expired ad not showing up there at all?

For the record, you should be seeing something like this:

expired-ad.png

You can then use the "renew ad" or the "end ad listing" buttons to finalize the ad.

/ warning: rant coming up

Stupid ad blockers! What incredible pieces of software.. Simply block every image that has "ads" in its path and hide every html element that contains 'ad' in its classname. That's impressive programming!

/ end of rant

Sorry, I'll go and add to my to-do list: rename all instances of "ad" on the site to "blabla".