If Z is a function of both X and Y, then one would expect it to be a 2D array. The fact that it's a vector leaves me to question how it was calculated and what it means conceptually. Without knowing that, there's no way to say how to fix it.
Consider the example:
x = linspace(-1,1,10);
y = linspace(-1,1,10);
z1 = x.^2 + y.^2; % this is a vector
z2 = x.^2 + y'.^2; % this is a 2D array
In this case, z2 is a 2D array describing a paraboloid over a rectangular domain. On the other hand, z1 describes the same paraboloid along the diagonal of the same domain (the orange line).
The second case (z2) is what you'd want to use with contourf().
contourf(x,y',z2)
Whereas z1 doesn't contain enough information for a contour plot. You'd normally just plot it.
plot(x,z1)
