I'll third (or fourth or fifth) that you should get out and ride regularly. In different conditions too. Don't be afraid of a light rain shower or some heat and humidity. You'll learn something about how to handle your bike and your body. Also, before setting out on a multi month tour at least try an overnight or two with your equipment to gain some experience with setting up camp, preparing food, working your stove, etc.
My first self-contained tour was at 15, camping in the panhandle of Florida with a group of 12 for a week. No sag wagons, had to buy and cook my own food. It was a real confidence booster and helped me realize I could push through my physical and mental barriers when necessary. Don't let the size of a cross country trip beat you down, it's just one day after another. After the first week or two you'll have 90% of the experience that you need to complete the job. The other 10% is improvisation.