Echo Effect is Reversed

That is a perfect example of a tutorial prepared by an enthusiast that poorly explains a very inefficient workflow for creating a write-on effect. I would give it a D. The reason you are having problems with the Echo parameters is that the explanation was not only inaccurate and misleading, but it left out critical information. Just changing the time offset to a negative number will change the direction of the echo from in front of the movement to behind it. You need to vet the folks presenting tutorials. This one is pretty awful.

There are a lot more efficient ways to more accurately animate a write-on effect using the trim paths animator on a shape layer and a couple of masks with animated opacity. If you insist on trying the echo effect then the way to accurately see through the track matte is to change the blend mode to set to Overlay or Screen.

Here's a recent thread with the workflow I would recommend: Issue with write-on animation effect Ae

I have done a fair number of these animations and both the workflow and rendering are going to take you a lot less time and be a lot more accurate using the techniques I outlined in the thread from April 23.

try setting echo time to a negative number