Replying to My dilemma...

okay, so my buddy called me about an hour ago to invite me to come with him to mammoth for a week after we get out of school. keep in mind i live in pennsylvania and go to college in new york. i have never been out west and dont see it happening anytime soon, simply because my family isn't that big into skiing. now, being a poor college student, i told him i didnt have the money to go and turns out his mom is paying for the whole thing, including for me to come. so theres one side. a free one week trip to mammoth for a kid who has never been out west and won't be going until he's on his own after college and grad school.

now...the other side. i faxed the confirmation for my summer internship YESTERDAY. i had the option of starting right when i got home from school or waiting a week, so that i could have some time to relax. i didnt have anything going on and need the money so i chose to start right away, and the fax that i just sent pretty much set that date in stone.

my question for you, newschoolers, is what do i do? do i call my future boss and beg to push my start date back a week and risk having them be pissed at me and just give my spot to someone else, thus eliminating my only source of income and a valuable experience? or do i give up a free one-week trip to mammoth? i feel like i dont really have a choice, but id like to have someone (cause god knows my parents arent going to) tell me what i want to hear.