Sounds like you have zoomed your screen a little. Hold down the CTRL key and scroll down with your mouse (assuming it has a scroll wheel or is a mighty mouse).
I figured it out. I went into the system preferences, the keyboard and mouse folder, then options folder. There was a place where I could reset how the screen image moves with the mouse. I don't know how it changed to begin with.....
Sounds like you have zoomed your screen a little. Hold down the CTRL key and scroll down with your mouse (assuming it has a scroll wheel or is a mighty mouse).