Simply don't believe that the Para offiocers involved would have acted in the way they were shown, nor that the Para's were quite so 'up for it' as they were shown to be. If the Army fired first, then I'm sure that it was cock-up rather than conspiracy.
I didn't watch closely, but didn't notice Martin McGuinness with his Tommy Gun shown, nor any one with nail bombs, nor any other gunmen. Even-handedness would surely dictate that all the accusations over Bloody Sunday should at least have been shown/mentioned.
What did we really expect from a TV drama, though? Truth?