It looks like the NORMDIST function on your sheet is taking the integral from 0 to z_score, which is one-sided. A two-sided test would take
z_score
(integral from 0 to z_score) + (integral from -z_score to infinity)
It looks like the NORMDIST function on your sheet is taking the integral from 0 to
z_score
, which is one-sided. A two-sided test would take