Hi,
You are not doing anything wrong. The crisp value you obtain is the result from the defuzzification process. In your case, the defuzzifier is the Centroid, which computes the centre of gravity of the fuzzy output, hence resulting in the mid-values you get. If you want the entire range, I suggest you move the terms such that their respective centroids cover the range you want the output to be in.
You may also find more information in the documentation available at http://fuzzylite.com/downloads.
Cheers.