Scooby,
Surely your bylaws have something about a quorum. A quorum for a vote would most certainly involve at least half the members.
One of the things that troubles me is that the principal had any say whatsoever in the way the vote is/was conducted. Isn't your PTO its own entity? With its own EIN number? I know that I've been very lucky with my own principal, she and I are friends as well colleagues, but we would never allow her to make the decisions for our organization simply because she is the principal. She attends as A)the principal and B)as a concerned parent. She does not make decisions for us or about us, other than to vote as a concerned parent, one of many.
I sympathize about your missing voters. I have come to find out that the parents who support me are the parents who work. The parents who cannot make meetings and volunteer at the school on a regular basis. My supporters are the ones who trust me to represent them during officer meetings when we are narrowing choices down to present at the general meetings. My supporters know what kind of job I did this last year, and so do I. Do I need a title to do great things for my school? No. And I'll tell you something:
Neither Do You. Have pride in yourself that you didn't cheat, lie or steal to win the election. Everyone else knows you didn't lie, cheat or steal the election. Hold your head up and move on. Get past this or it will eat you up. Get your supporters together and attend the meetings and vote in the stuff you would have picked anyway. Mostly, be proud of the job you've done and will do. Take it to the next level by moving past this one. Be a great example for the kids by congratulating the winners and then, move on to bigger, better and brighter things.