rude much

I was eating at a diner for my sisters birthday and before we left our mother told us that we need to behave there. When we were all done with our food I was walking out to start the car as my sister was paying and the lady there asked "do you need help" and I said no then she got mad at me again and repeated herself. But she was angry and had a harsh tone. I then said "no thank you" and she got mad at me and walked off.