Stop using any whiten toothpaste and do not use any strips either. You do not want to whiten you teeth why you still have braces. You are whiten only what is not covered by your braces. Once you have your braces removed it will possibly show up darker and you will be left with strips on your teeth. Wait until you have your braces removed then see a dentist to correctly whiten your teeth.
Do however in the mean time, try to be better at brushing your teeth thoroughly. You do not want to have other issues like cavities or gingivitis.