First of all, you want to move your task initialization code outside of the loop. You only need to initialize once before the loop. You should also clear the task after the loop.
Secondly, you stated that you wanted to sample every ms. That means you should set your sample rate to 1000, not 800. I would also recommend using the Continuous Samples acquisition and don't wire the number of samples in the DAQmx Timing VI.
Thirdly, I don't know why you changed the array into a cluster to get a single waveform. All you needed was the Index Array.
Attached is a quickly modified version of your program. See if this does what you need.
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