puh... I have to reoverthink your post, because I couldn´t figure out what you tried to say (sry I´m foreign).
I want to have the screen pan/scroll down to show the entire image
Sry. You can´t move the "screen", but only move all items into the screens. A camera move is only possible in After Effects.
with the roll preset, it not not does that but starts over from the beggining.
Aha... The picture moves...but nothing blank comes up, but the image again?
So how can I achieve a scroll down affect from point A (on the image not black) to point B (on the image) without the thing going back to point A?
Don´t use roll. Think about the basic things and settings:
-Select your image ("click on the timeline on it")
-Open the effects control "window" (left to the preview monitor)
-At the top stands "motion". Click on it
The first parameters are for the postition and that is what you want. Click onto the clock to activate the keyframes for this parameters (you know what keyframes in effects are?)
-Move in the timeline where your picture reaches the final position.
-Edit the coordinates from the position in the effects control - motion section
Your image should now move to this position.
I recommend you to look at the whole motion section. It´s quite usefull for effects.