You were getting 7 signals 7 points long because you are only indexing out 7 waveforms (you dragged down the Index array to give you 7 outputs), but you were wiring up nothing to the index inputs, so that gave you each row of the 100 row x 7 column array by default. Each row (and you are only grabbing the first 7 rows), gave you only 7 elements because there are only 7 columns.
If you don't believe it, then put some array indicators in your code expanded. Also put in some array size functions and indicators on that so you can see exactly how big your arrays are at every step of the way.