I think you're anxious because you don't want to leave elementary school behind and moving on to something new without knowing what to expect is not always obvious. That's OK!
They make it sound as a big deal, but trust me it's not. Everybody can make it through and in the end you'll be glad you did.
So, be positive about it...

I am sure you're ready for it even though you think you're not. Be happy to move on to something new without being anxious!