I am feeling that way as I return to my job after two years! I think it´s only natural if your personality is inclined that way - teachers want perfection!
Focus on doing practical things to keep your mind off of the anxiety. Get the cupboards stocked so you don´t need to do a big supermarket shop when you´re knackered at the end of week one, get household chores out of the way, get laundry and ironing and any dry-cleaning done so that you have your clothes sorted, prepare a clear space at home for marking, get your USB, coffee mug, emergency bag of tampons*, etc. ready to take into school...
Also if you wear a watch make sure the battery is working properly.
You can even do stuff like a trial run of getting there one morning, do a recce of the area (if it´s one you don´t know well) to see where things like cashpoints and post offices are (if you tend to use those things), plus arrange hair etc. appointments while it´s still holiday time.
Good luck! You will be fab and knock them - figuratively - dead!
(*Please tell me I´m not the only person who keeps this kind of thing at work?!)