1/2 marathon in May and getting worried

Don't give up!  I just did my first half today and had a similar problem as you.  My running buddy got a job (so couldn't train with me) and the weather here has been horrible, so the last month my training slacked big time.  My longest training run was 10 miles on the treadmill and after I felt like I was going to die!  Honestly, the 10 miles took so much out of me  I dropped back to about 1-2 days a week of training, just trying to do my long tapering run on the weekends... 8 miles then 5... 

Anyway, doing a half is an awesome accomplishment and who cares if the marathoners are driving home while you're still finishing... you are doing more than most people are going to do!  I can personally say I only know a few people who have ever had the courage to do either a half or full. 

BTW, lots of people fatter than me passed me today... lots of MUCH older people passed me right by, but that's okay, because this is my battle and it's unique too me.  Remember

Success isn't how far you got, but the distance you traveled from where you started.