Relief is what you need, and fast. You can find over-the-counter antiseptic creams, lozenges and mouthwashes at your local pharmacy to help relieve canker sore pain.
Some examples include products such as Orabase with Benzocaine, which covers the surface of the sore like an "oral bandage." Keeping it coated will help prevent it from getting infected. Products with xylocaine, a local anesthetic, can also dull the pain.