You'll be fine, if you can cook a roast chicken dinner then you can do Christmas.
You can prep veg on xmas eve or 1st thing better yet get your OH on prep duty, keep all the veg and potatoes in cold water. If you plan Turkey I should get a crown, so simple to cook.
You could get things like ready made red cabbage, stuffing balls, carrot batons to make things easier.
Get people to help, someone else can lay the table, and make it clear you are not responsible for clearing up.
Don't panic, don't expect perfection and sip a nice glass of something while you cook to relax you but don't go mad!
Make a lost of the cooking times and write a timetable, it will pay off so , Turkey in oven at 10am (or whatever) and so on.
The turkey can be under foil and clean towels resting for a good 45 minutes while you roast the potatoes and finish off.
Pigs in blankets, you need hundreds!
Think about foil, cranberry sauce, gravy, bread sauce, all those extras you may need but nobody will have the day ruined if you forget something.