Should my parents be mad at me?

Ok so I had to mop the floors and do the dishes today. I mopped the floor sorta quickly and did the dishes but on my way out I hit the wrong button on the dishwasher and they didn't go through. My parents want to ground me until further notice but there have been several occasions where my sisters didn't do their chores and got to go out. What should I say to them to make them understand that I made a mistake and it won't happen again. They also got mad at me for crying. Are they being unreasonable or should I just have to clean the house tomorrow and not be grounded.