They do have a direction, data goes in one end and comes out the other. You need to find which side it it. The string I have is labeled right on the frosty covering for each pixel: a small arrow that points up or down.
I'm only familiar with the FastSPI library so:
Did you connect the string's data wire to pin 11 as your code states?
How are you powering the string? 150 pixels out of any AVR pin is too much. Even one pixel at 100% duty cycle for all three channels will be too much.