Well, it may be best to look at it this way: You have a chance to make some really substantial changes and turn things around. But it will take time, which is OK.
You might want to start by just reaching out to parents. How did that first meeting go? Can you send thank you notes to the parents who did show up? Then you can try sending out an email or letter to the school community to let them know of the PTO's plans for the school year and welcome input, feedback and participation.
Do you have any fall events planned? It would be great to plan a simple, low-cost event -- maybe a pot luck or spaghetti supper -- not so much to raise money but to give families an opportunity to connect.
As far as the principal is concerned, try reaching out to him/her and simply say, I want this relationship to work -- we both have the kid's best interests at heart -- so how can we make things work? If you straight out ask how to work together, you may get a surprisingly positive response.
Here are a few article links that you might find helpful:
For building parent involvement:
13 Keys to Strong Involvement
Involvement, Step by Step
For working with the principal:
Make the Principal Your Partner
Negotiating With the Principal
13 Keys to Strong Involvement : https:/classic.ptotoday.com//pto-today-articles/article/5-13-keys-to-strong-involvement
Involvement, Step by Step : https:/classic.ptotoday.com//pto-today-articles/article/414-involvement-step-by-step
Make the Principal Your Partner : https:/classic.ptotoday.com//pto-today-articles/article/209-make-the-principal-your-partner
Negotiating With the Principal : https:/classic.ptotoday.com//pto-today-articles/article/176-negotiating-with-the-principal