You can add 5 more segments for North America (you only have one, MEX-DFW). So you could do MEX-DFW-ANC-DFW-YVR-JFK for example, remember the ticket is valid for 12 months from the date of the 1st segment). Or you could do MEX-DFW and then BOS-MIA-LAX-ORD-BOS later, if you wanted to get home from DFW. Your RTW doesn't end until you return to JFK, it seems a shame not to use the remaining segments for another trip.