I dont know how to talk to my parents about this?

Im 12 and nearly at the end of my first year at high school. At the end of the year, theres an off timetable week, where we can either go on a 5 day trip or stay at school and do activities. Im meant to be going to paris in two weeks, with all my friends (whom i have been having problems with lately and feeling a bit out of the group). My parents have paid about £475 to let me go, and i feel soooo guilty, because over the last couple of months i have been DREADING having to go. I know im soooo selfish, and i feel terrible, but i feel like ill have no friends there, and just not be able to enjoy myself properly. I know i cant talk to my parents, what are they gonna think when i just say ‘sorry, but that trip you paid £475 for me to go on, i dont wanna go any more!!’. I dont know what to do, they just get really angry whenever i even HINT that i dont want to go…please please help me, i know im a selfish, ungrateful brat, but i have never been away from home on my own for that long before, it will be even worse without any friends to talk to…