The default terminal width for an IOS-based router like yours is 80 characters. You can set it manually as described here:
http://www.cisco.com/c/en/us/td/docs/ios/12_2/configfun/configuration/guide/ffun_c/fcf003.html#wp1004641
Another item might be your settings in your terminal emulation program. They also have local settings that can affect what you see on the screen. Have you tried an alternative program?
