The categories on the e-wang chart aren't accurate and aren't intended to represent performance potential. Dr Coggan has stated that chart should only be used for power profiling of individual athletes. Also, there are two versions of the chart. The one in the 2nd edition of the book is the newer one.
It's common in my area (NorCal) for riders to have FTPs that are 1-2 categories higher than their actual category.
Edit: +1 to everything Shovelhd says.
Also, you did pretty well for your first time- didn't get dropped, was active in the race, learned something. Most people don't do any of those in their first race.