Completely agree with meecal - always book one way tickets.

Also - I keep a very simple spreadsheet with all of my reward travel (along with the points each flight costs). Take a few minutes to set it up. Update it regularly. Always book one way tickets. You will never have a problem like this again.

Added bonus - the spreadsheet makes it very to see if any fares dropped vs. original booking cost. I've probably saved 30,000 points over the last couple of years from this practice.