Whos in the wrong? Fathers day drama

My step mom texted me and my brother today asking if we could go to a dinner at 12 Sunday. I told her I couldnt go because of school. Thats all I could say because i was at work and didnt have time to respond.

Anyway..as soon as i get home from work she starts acusing me saying all of his kids don't care about him. That i dont make time to talk to him, that im irresponsible for not planing ahead for fathers day. Basically saying that because i couldn't attend a last min dinner that I dont care about him. Ect. Just going ham on me. She made all of these assumptions and painted me as the bad guy.

Its not like I dont wanna go, its just last minute and I have stuff to do.

I cant go because of MANY reasons:

1.) I get off work 9AM that morning, the dinner is at 12.

2.) I was told LAST MINUTE about the dinner.

3.) I have school work due that day. Im in a cram course so its 10x the ammount of school work.

4.) What she DOESNT know is I got my dad two gifts. Which is way more than what we usually do. Most of the time we just get a card that everyone signs. But i actually got him gifts this year.

5.) I do make time to talk to him, neither of us know what to say to eachother but that doesnt mean I dont try.

Its like what im doing isnt good enough, she's notorious for making my dad feel like that.