First, if you really waited this long to buy your camping pass, that's your dumb-ass fault. They sell out EVERY YEAR around this time, so you should know better, especially if you have gone in the past.
Second, no one is going to trade you a camping pass for your 'single day ticket' because there is no such thing as a single day ticket this year. And likewise no one is going to trade you a single day ticket in exchange for your extra camping pass, because you do not have a single day ticket and are a giant douche for the above stated reason.
Thank you for your cooperation.