I have problems with my step-mom...can someone advise?

Only you know if you have truly done something wrong. If you feel you have done something wrong then a gesture without an ulterior motive would be appropriate. Sometimes it is hardest to admit to yourself that you were wrong. And sometimes other people won't believe that you have changed after one honest effort. But just by what you wrote I think there is more to the story and you feel guilty and think you should do something. Only you can make that decision. My advice is that you spend some time talking to your step mom after she has calmed down and work through it. Bless you... I have every faith that you will do the right thing!!