The way you're doing it, you are adding two rows to the 2D array with each iteration. In frame 1, you're taking the existing 2D array and concantanating 2 1D arrays. Instead, just use the build array with two inputs and do not concantanate. You could also use a chart like in the attached example.
Also, you said you created a second Y axis scale but the posted example doesn't have this.