Friends problem! helpppp?

ok so i have a group of 6 best friends and we all go to overnight camp which is coming up in a couple of days which means we all won't be together this summer. Before camp we usually do something really fun for like our last time really going out and doing something just the 6 of us before the summer. Tonight they wanted to go to the city (philly) but two of us can't go, one being me. but yet, the four of them are still going and aren't re scheduling. And i think it's kind of rude because the whole point of us going was for the 6 of us to do something fun but two of us can't go! I know you guys are maybe thinking i'm just getting mad because it's me who can't go but last year when we planned this one person couldn't go and i stuck up for her and said we should re schedule since she can't go. (just so you guys know i'm not just getting mad b/c it's me) also it's not like this is a regular hangout in the middle of the year where if people can't go it's not a big deal. bc if it was that i wouldn't care. so i'm just wondering if you guys think im getting mad for nothing or if i have a reason to be bothered? and i obviously know the girls well and know that if one of them couldn't go and the rest of us could they would be pissed.