I'm in my 11th year of teaching, and I cry sometime each year! It happens to everybody, and everybody has moments when the class seems hopelessly out of control.
You can keep some high-interest papers held back for such times.....some of those very complicated drawings and colored pencils to color them in with would be great..........just to pull out to get them seated and quiet. Afterwards, let them know that the way they are right now is how you need them in order to teach them. Tell them they can have these "special" things from time to time if you can have their attention when needed.
Also, be sure you are doing lots of positive feedback during the day. There will usually be SOMEONE you can point out as doing SOMETHING well. A simple, "I like the way June is ..........." works. Be sure not to choose the "scapegoat" of the class for that. They need it too, but more privately would work better for them. Also, more private for the "tough guy", who is usually hiding huge insecurities. You should aim for 3-5 times more positives than negatives during any period. You can tally them for yourself and see what you're doing.
Don't worry about the principal if you can help it. They know how it is, and are looking for what you do well. There's plenty of good stuff going on too.
5th is a tough age. I have them in after school science. You can appeal to their humanity, though, and they will usually deliver. Everyone gathering in an intimate little group to talk things over can really help. Point out what you need from them and why, the consequences when they don't deliver, and include how you feel..........most do listen. If there is a ringleader or two, send them on a special errand and talk to the rest about the particular challenges that child is facing with behavior, and how they can help you. At my level, I ask the kids to try to look another way, get up to sharpen a pencil, or get a new book.........whatever they need to do to pull themselves away from being an audience when a particular child is being inappropriate or disruptive.
Anyway, not meaning to sound preachy, just some advice and I hope it helps!