Start=50 and limit=60 means that your addresses START at 192.168.0.50 and are LIMITed by 60 successive addresses in total. In practice that means you will have 192.168.0.50 through 192.168.0.109 in use (60 addresses in total).
If you want to limit your address range from 192.168.0.50 through 192.168.0.60 as you seem to want to do, your START should again be 50, but your LIMIT should be 11 for the 11 addresses in total, NOT the 60 you have selected right now.