It's in the CGC rules that if a dog blows only 1 test they can try again that night, if they blow 2 or more they have to come back another day to retest.
Recall isn't that hard. Never be angry when you call your dog and he/she comes, it can save their life so always be happy they came to you. And use high value treats, my dogs love the chicken jerky from Costco, but left over meats in the fridge work too. Have someone hold you dog (if they don't know stay), walk away a bit and call their name, when they come, treat and praise the dog. Gradually add distance. It won't take the dog long to learn that coming when you call their names means good things are going to happen. A solid recall has saved me from hours of searching the neighborhood when my dogs escaped the yard, and I live right next to a major highway so it's probably saved my dogs lives as well!