Assign all data partitions to a single node

We have an A300 with a single shelf of disk. We want to maximize our data capacity in a single aggregate. The disk size is 3.8TB SSD. All of the scenarios run in the sizing tool by our VARs say we can get a single aggregate across two 23 disk raid groups for a total of 71.49 TB. However when I try to build the aggregate I am only able to add the 23. How do I add the other 23?