Hydrogen peroxide has cleansing, antiseptic, whitening and deodorising properties. Despite these benefits, it is not recommended for daily use in the mouth. Rinsing or swabbing the mouth with a hydrogen peroxide solution is beneficial for inflamed gums and even for the throat, but 3% is a very high concentration and needs to be diluted. The recommended concentration for use in the mouth is 1% hydrogen peroxide, and it must never be swallowed. Because of the risk of swallowing it, rinsing with hydrogen peroxide is not recommended more than 2–3 times a month, and it is best to limit its use to times when there is inflammation in the mouth. Its concentration isn't high enough for you to see any whitening effect on your teeth, and it is dangerous if swallowed – so don't use it for whitening!
This answer is for general information. Your own case needs an examination by an orthodontist.