PAT in DAT Achiever has been designed to prepare candidates for the worse. It's not bad to get a 16, but there truly remains much for you to continue working harder on.
Go through each question carefully and ask yourself how to better overcome the same weaknesses the next time you're faced with these again. When my buddies and I studied together for the PAT, none of us got a better score than 18 in the first test from this software. But we made full use of the solutions given and discussed those problems actively among ourselves... with truly great scores achieved in the real test eventually.
Post some specific questions here, possibly those coming from the test itself, and I'm sure the SDNers will be willing to help answer with.. That way, you can end up improving yourself on the PAT much quicker. 🙂