Currently the Goals for petitions counts all of the petition signatures collected on the site, regardless of which petition the signatures were collected on. It's not possible to track the progress of individual petitions, only your cumulative results.
When creating a new petition Goal, please add an option to select which petition you want the Goal to represent. This would make the NationBuilder Goals feature more useful.
This is something we will consider but does not have a timeline at the moment.
However we are paying close attention to the most popular suggestions so please share and encourage others to follow and comment!