It is set from start to end and the problem is still occuring.

Are you sure you don't mean the red "play" marker?  If so, you have a few options.

One is to zoom out far enough that the screen doesn't move forward during the segment you're working on.

If you hit the P key, the Program Settings dialog box will appear.  On the General tab, the first section should be called "Arranger".  The first section may be titled "Autoscroll during playback:".  This controls the behavior of the play marker/line.

The default is set to "Fast" - the play marker scrolls across the entire arranger and the screen jumps to the next "page" (so to speak) when it reaches the right side.

With the "Slow" setting, the screen will jump to the next "page" before it gets to the end and continues in the same manner still showing a short section of the previous "page"

In the Off setting, the screen does not scroll at all when the play marker/line reaches the right end of the arranger screen.  In this case, you can use the scroll bar to scroll the screen manually, or choose to leave the section showing as is.  You can "reset" the red play marker simply by clicking on the desired location on the timeline at the top of the arranger.