Ask your stepmom to help you control your portions. Let her know that her cooking is hard to resist! (That's an honest compliment!) I think she will appreciate your confidence and a chance to be your ally.
My dad got remarried and my step mom keeps giving me food and now I am a lot fatter. I can't tell her no because I live here food. Please help?
Watch your calories. Eat sensible amounts of her nourishing food. Take time to enjoy the food. And “make home meals a pleasant experience.”
I'm thinking your are old enough to ask her to not such give you such big portions and tell her why. Nothing wrong with liking her food for meals .. You can even compliment her on it .. But, just simply ask her to kindly limit the portions .. OR .. Let you help yourself so YOU can limit your portion.
You can talk to your dad first if you feel more comfortable that way rather than talking directly to her at first.
Your stepmom may be expecting you to tell her when you have had enough to eat.
And your dad may just think you really like to eat your stepmom's cooking rather than notice she is giving you more food than you like to eat unless you tell him.
And he may just tell you to "just tell her you've had enough."
I'm thinking this can be easily fixed.