OP,
Just go. What you have to loose?
What would you otherwise have spent the night doing anyways? Surfing the web?
This isn't the 70's anymore. I'm sure over half of your Grad class is going, without a "prom date"
Enjoy the dinner, take some pictures with your friends. With the people at your table.
And maybe you'll find a girl that you will dance with you, on the night of.