I'm a 15 year old boy and I need help to realize if what I did was really bad or is not even a big deal?

So I wake up at 8:45 in the morning and my mom drives me to my doctor's appointment at 10. That takes 40 minutes. Afterwords my mom takes me to the grocery store at 11 to get food for dinner. She says she's picking up a couple things. I said I'll just stay in the car and sleep because I was tired from going to bed at 2 in the morning. So I take a nap, listen to my ipod and I get bored. It begins to get very hot and I open my door. I check the time and it is 11:30, I think it's been kind of long but maybe she's just taking her time and she'll be out any second. 30 minutes go by and I feel kind of sick and very hungry. So I leave her a note saying "You took too long, I walked home because I am hungry." and I walk home. It takes 10 minutes to walk to my house from the store and on my way my mom pes me up and offers me a ride. I was very angry and I said "no I'm fine." So I finally make it home and my mom yells at me saying the note I left was very impersonal and my dad called me a dumb @%% and my brother was telling me I should leave. I went into the kitchen to make myself something to eat and my mom is very upset. She continues to ask me why I did that and that she would have never done that to her parents. She seemed embarred because she was telling me not to tell any of my friends about this but she turned around and said wait till Mike (My oldest brother living on his own) hears about this. I was honestly astonished at my mom's behavior. She continues to tell me she was flabbergasted and she yells at me some more. I tell her it wasn't anything personal, I was just hungry. My brother (He's 16 living with us) steps in and says "Do you care about anyone but yourself?" I didn't know what to say. My mom goes into the garage and my brother follows. I go in 5 minutes later and my mom is crying and I hear my brother as I open the door telling her that I don't care about anything. He intercepts me from trying to talk to my mom and starts making up stuff about me. My mom tells me she is going through menopause and she is very angry at me still and I tell her that it's ok. She starts crying and my brother yells at me and i just leave the room cause i think they are just acting like idiots. Can anyone please give me their opinion on this? Am I a bad kid or are is everyone I live with overreacting?