There is currently no way to delete an event from your activity feed.
However, though you can't remove the artwork from your activity feed, you can "hide" an unwanted event from view by adding a new series of events to your timeline. Your old activity will eventually will be replaced (and will no longer be viewable) when you add new activity. For example, you can: favorite additional artworks, follow the activity of other artists and collectors; create a collection, upload new artworks.
We hope this helps! We apologize for these current limitations and assure you that we're working to improve our site's functions on a daily basis.