Many that have tried the baking soda/hydrogen peroxide mix have complained about bleeding gums and the seemingly white burns that proceed them. This is actually an indicator that you have not been brushing or flossing correctly in the past.
It is normal that the mixture will cause this reaction as it is fighting the start of gingivitis in your mouth. It may take about two weeks for the bleeding and swelling to stop. The white burns will not remain long after a single brushing with the mixture, maybe 5 mins or so and then your gums should go back to their pink, fleshly color. I would take two weeks of minimal discomfort any day over developing gingivitis or a worse gum disease. Be sure to use 3% HP. I floss first sing the G.U.M. mini flossers...this is imperative!!! If you don't floss, you are already losing half the battle in fight gum disease and bad breathe.
Next, I take a small cup and pour a teaspoon of baking soda and slowly add HP until it is pasty like toothpaste. Gently brush in circles for about 2/3 minutes. Rinse out with water. Some may follow up with toothpaste...do as you feel necessary. Lastly, rinse with HP and then water again!!!