I think your formula for scrolling is wrong.
Imagine you moved your finger 100px to the right, TravelledPositionX=100
On every tick your screen will be scrolled by 100px, that's 6000px per second!
You should probably save scrollx, scrolly into variables "StartScrollX", "StartScrollY" on touch start, and then use these variables:
Set scroll X to (StartScrollX+TravelledPositionX)