You've got the publisher, written the book and now it's done.
There's no room for doubt.
You've done it.
You're an author.
For a number of reasons -
Now you've written that book, take a rest. Read a good book. Relax. Chill out. You've earned it.
Hopefully the person jumping out of your cake won't look as bored as these two! For a major scene in my book, How Kirsty Gets Her...