Kristin, what a cool goal and how great you'll feel Sunday when you've done it!!
I'm betting that those pre-race jitters will ease as soon as you settle into your pace. As a former runner myself, I know that nothing quite beats that phase about 20-25 minutes in, when you feel yourself comfortably moving to the beat of your own inner rhythm.
I bet it will also be extraordinary to re-greet your inner self on the half-marathon path. She is waiting there for you, shoes laced up, face flushed in anticipation, a twinkle in her eye. When the two of you get to run together again, I have a feeling that you'll be energized, not fatigued. She missed you, too.
Good luck, have a blast, and please come back and let us know how it goes!