At a minimum, make the day before your hike a rest day, meaning no training on that day. Consider taking two days off prior to your hike. This way, your leg muscles will be well-rested and you'll be ready to conquer your goal.
If this training schedule seems a little aggressive, add another week or two up front and make the increase in miles a little more gradual.
Cross TrainingIf you don't like the idea of walking so much, throw in a little cross-training. Running is an excellent alternative. Cycling, treadmills and stair climbers also provide great cross-training/cardio workouts as well. However, don't rely solely on these exercises. You'll still need to do a long walk at least once a week.
On the day of your hike, take enough food and water with you to keep your fuel and hydration levels up. See my article about proper hydration and learn how to beat the heat on summer hikes.
A little preparation beforehand will go a long way on the day of your big hike. Your training will give you the confidence to persevere and you'll feel much better when you arrive back at the trailhead. You may even have a little energy left in the reserve tank to celebrate your accomplishment.
Be prepared and book your campsite.