A lot can happen on race day that is unexpected...good and bad. I think to Nancy's point, you really shouldn't get too focused on a time goal for your first race. My first 5k I ran with a bunch of friends, all our first race, and they were all do dissapointed with their times. There is nothing more annoying than listening to someone, who ran faster then you, complain about their finish time!
Do I think you can finish in 27, maybe...but I'd also caution you not expect it. Just enjoy the exerience and know it's a baseline for you to improve upon!
Patience and Fortitude - Mom
There ain't a thing I've faced that's been too much for me - Classified "Inner Ninja"