You forgot the parts
1. Select the key points/time points you want to copy, you can window select in the timeline.
2. RMB, copy and paste.
3. Select the newly created key points, RMB, choose reverse path.
You may have to select the points of the reversed path, and moved them as a group by cut/paste, or something like that, to get them where you want in the timeline, but this should get you close.