30 kilometers running

Since the Kobe marathon came closer, I ran 30kilometers .
I ran two sets of my 6 kilometers course and my 10 kilometers course and stopped when I run just 30 kilometers.
The limit came to me about 25 kilometers on the way and I took a rest for about 10 minutes.
It may have been dehydration symptoms.
There was a vending machine selling 500 ml bottle of Aminovalue, so I drank it slowly for 10 minutes and recovered, I fnished to run 30 kilometers.
It took 3 hours 45 minutes, so I think I can finish in the Kobe Marathon, but I wonder if it is impossible for me to finish within five hours this year as well?