I have had some problems when running DOSbox fullscreen.

First of all I have a Dell m1210 with a nVidia GeForce Go 7400 and running DOSbox 0.70. The problem is that when I make DOSbox to go fullscreen the screen gets really small at the center of the screen. I read somewhere in this forum that you need to change some parameters in the DOSbox.conf file, but the "fullfixed" parameter (which is one that needs to be changed) is missing in my config file. This is what I got:

fullscreen=true
fulldouble=false
fullresolution=original
windowresolution=original
output=surface
autolock=true
sensitivity=100
waitonerror=true
priority=higher,normal
mapperfile=mapper.txt
usescancodes=true

What should I do to get a correct fullscreen?