This is a family based question. Please don't criticize me for any misspellings, I typed this from my phone.?

I'm asking this just to get back information. Yes, I know I should be thankful that I have family, and food and many other things (and I am), but I'm a just asking for an answer to this question. Alright I am a 15 year old with two little brothers (12 and 10) and while the 10 year old is fairly annoying and my parents never punish him I get by. Now in addition to this my parents are divorced and I am currently on vacation with my dad and his girlfriend in New York city. The thing is my dad's girlfriend brought her even younger two children, and I am just wondering if it is ok that I feel a little bit pissed off. Again, this is my first real trip out of my home state (even though my dad goes on numerous trips out of state), I have never been on a trip with any of my friends (I have however been on several trips with my annoying cousins), even though my dad has been planning this trip for months he never told us that his girlfriend was coming until the day before we left (he didn't even tell us that his girlfriend was coming, one of her kids did), and all the attractions I wanted to see in New York, a performance of Hamlet, the Metropolitan Museum of Art, etc., have been replaced by more child friendly events (a children's play, going to a Toys R Us, etc.). In addition to all this I have been perfectly kind to my dad's girlfriend's children, and I have not complained one bit (my dad just yells at me one I try to). And in addition to all this I have multiple tests coming up in school (I'm on a wierd accelerated program where I have a test in at least one cl every single day) and multiple clubs in my school that expect me to complete some form of work that I am completely unprepared for because I am missing two days of school to be on this trip. Is it right that I am a little bit pissed off at this whole situation? Do you think I should have to go on trips like this? Thank you for responding.