What am I supposed to do? ED troubles?

So it's fathers day and my mum thought it would be nice if I took my dad out for lunch, i don't much like talking to her so i just agreed so she would leave me alone. the thing now is i have to actually take my dad out to eat and well i have an eating disorder. usually if i eat at all, i do it privately and then most likely i will puke it up, but today i am sick and my throat is really hurting so i dont really want to throw up at all today. besides im more of an anorexic than bulimic. anyways, my dad is barely home so he doesn't really notice that i dont eat, but if he does notice for once he usually makes a huge deal out of it and will start yelling. being in public wont stop him from making a scene so i dont know what to do if i take him out...which i have to. so im just asking what should i do, because i dont want to eat and i dont want to have a scene with my day in a restaurant and I HAVE TO TAKE HIM OUT. i didn't get him anything else..