Two things I've found:
-- Jitters pretty much go away as soon as I'm on the road. I then shift into working things out day to day. Perhaps there is some upcoming thing I might work out (e.g. that squeak in my drive train or whether an upcoming holiday weekend results in all campgrounds being full...) but it is different
-- Jitters happen a lot less and for bigger things. For example, I recall more jitters before my first cross-country trip flying to Portland, than I do years later flying to Prudhoe Bay, despite PB being much more remote

Have a great trip and enjoy the ride!