Even professional runners have bad runs. It's called "bonking," and it happens to all of us. The best thing you can do is 1) not beat yourself up over it in the least, and 2) consider if any factors within your control could have contributed to it (for instance, I've learned that drinking any soda before a run destroys me, as does eating too many high fiber foods--but I still have crappy runs for no reason at all once in a while).
But seriously, remember that it is just one run. The more you make running a habit, the more the occasional bad run will pale in comparison into the many normal runs you'll end up having. It's great that you finished and you'll probably feel better next time.
3/16: Rock‘n Roll USA Half Marathon
5/18: Maryland Warrior Dash
6/1: Virginia Wine Country Half Marathon
| June Minutes: 0