Have a great time! I'd agree with the standard corporate strategy of begging forgiveness
.
And I'd like to put in my $0.02 for what will likely be your question after completing this one: "What's next?"
Most people seem to think of a 5K as a "beginner" race and decide to try for a 10K next. Then they try a 1/2 marathon and finally a marathon. I don't exactly agree with that, however, because a 5K can be a great, competitive
race if you decide to train for it. Getting in shape for 5K racing can sometimes be a bit more fun than just getting in shape to complete longer and longer distances. You'll want to focus on some more speed and strength training than just going out every day to rack up miles.
I lament that for many events the 5K hardly has any serious competitors so when I do one I'm out by myself most of the time: either left way behind by someone a whole lot faster than me or easily winning the race (I can do about 21:00). I often am forced to do at least a 10K or longer to get more of a competitive field where I can enjoy the fun of "battling it out" with someone evenly matched to my ability. Then again, I live in a rural area so most races here are pretty thin for participants anyway. And I ran XC in high school which was a 5K event twice a week so the distance is somewhat nostalgic for me.
That's my pitch, anyway: the next step doesn't need to be just completing a longer race. Just like a golfer continually trying to refine their swing and improve their score you could try to refine your 5K by whittling down your time and upping your speed. And then, almost as a side-effect, if you wanted to do a 10K or longer you'll have a nice base of speed and strength on which to build more endurance.