
I entered five classes with my Junior bitch at our club champ show(It is often common to enter lost of classes and there are points trophies for the do winning most points on the day). I won all five and the CC and RBIS, so ti can happen.
As already said if they are unbeaten by another puppy they can still challenge for BP.
You cannot withdraw from breed classes only variety.
As a seen dog you will just stand to one side, and may be asked to move again with the class at the end or individually if the judge is considering including you in the new classes placings, so it isn't too tiring, and you can relax your dog until the rest of the class are seen.