Owies! Canker sores really aren't something to worry about unless you seem to get them often. They can be brought on by stress or diet (folic acid, b12 or iron deficiencies, or food allergies), and usually take about 2 weeks to heal completely.

You can either get something OTC to use on them during that time or try the following:
2 ounces of hydrogen peroxide and 2 ounces of water OR
4 ounces of water mixed with 1 teaspoon of salt and 1 teaspoon of baking soda.

Rinse your mouth well with either of these (using all of the solution) and wait about 1/2 hour before eating or brushing.

Good luck and keep us posted!