Nervous

With it being only 2 days until the marathon, the only word that can describe how I feel and will feel for the next 2 days is NERVOUS. 
Nervous: highly excitable; unnaturally or acutely uneasy or apprehensive. 
When I start out training, there is one thing that is in my mind, typically, and that is, just have fun!  Run because you like to!  And because you want to!  No one said you had to!  Then as training goes on, my highly competitive side takes over just like a jeckyll and hyde...or maybe in my case bipolar! LOL!  Well, whatever you want to call it, it evolves as I progress through the 18 weeks of training.  Then by the time the week is here, I feel nervous and sick and wonder why I do this year after year.  I wonder sometimes why I bother when I don't feel like I get any better at it.  If I don't get any better what is all the training for?  I have been told by almost everyone I have ever talked to about running that I am too hard on myself and that I should be happy to just finish.  I'd like to think that, but the truth is, I feel like I should be harder on myself.  How do I obtain any goal if I go easy?  If I don't have a goal (time) in mind then what point is there?  They call it a race for a reason don't they?  Then reality sets in and I have to understand that my biggest competitor is only myself and that no matter how fast or slow I might run, I am doing it because I can.  As long as there is a breath left in me, I will run....