This kind of thing seems to happen frequently in volunteer organizations, in both my own experience and the experience of other friends who volunteer. Person A volunteers to do a job, does it well, and Person B comes along with a boatload of overwhelming criticism and completely different vision about how the task should be done (usually requiring 2-10x as much time/effort as the volunteer signed up for).

So no real advice, just an observation - don't take it too personally or feel bad about the great work you have been doing for the PTO. This is about the principal, not you. How did your first meeting go and what was the PTO chair's response to this situation?