As you prepare for the marathon it is important you maintain a positive attitude. Always believe you will be able to finish the race, you can do this by mentally visualizing yourself in the race and crossing the finish line.
Running is never easy for anyone so make sure your training is challenging enough: run hills and do speed work so that you can get used to the feeling of running under stress.
Have 100% confidence on your ability to run and finish a marathon. And the only way you can have absolute confidence is to got out and train, train and train hard. Lastly keep yourself healthy and have a positive attitude the week before the race.