For a function F(z) to qualify as a CDF,
- The function must be monotonic: F(z) ≥ F(a) for all z>a
- The function must be zero at the low end of the range: F(zmin) = 0
- The function must be one at the high end of the rangeL F(zmax) = 1.
Given that, does your result look like a CDF?
A couple of hints:
1. Your limits of integration aren't right.
2. What values can z take on? Can it be a large negative number? A large positive number? Zero?