How to convince my parents to let me sell my car?

For High School graduation my parents sai I could "pick" out the car I wanted. I had my choices of a Mercedes-Benz 2001-2002 C 320, 2000-2002 E55 AMG or a 2000-2002 CLK 320 or 430. They said all those were an fine choice since they have both owned nothing but Mercedes since 1980. Summer went on and on and we looked and looked and I found many cars that I loved and every car I test drove or looked at they had an excuse on why It was no good. One day I came home and there was a 2000 Mercedes C280 "Sport" edition sitting in my drive way. I HATED SURPRISES FROM DAY ONE. I looked at it knowing that it was not the car I wanted or asked for and I specificly told them "DO NOT BUY ME FIRST GENERATION C CLASS BECAUSE THEY ARE TOO SMALL AND FOR THAT PRICE I CAN BUY SOMETHING WAY BETTER, CLK OR E CLASS) There I looked at the car and I have never drove it ever. I took it out for a test drive and hated it and complained all about thinking they would get the idea but it went over their heads. Now Im stuck with a 2000 C280 with 53,000 miles. I dont like because its too small, tooo cheap on the inside, poor performance and its a pain in the ass to maintaine. My parents have owned almost every type of Mercedes.(E320,SL600,CL500,300SEL,500SEC,300SD) You name it and we have never had any I REPET ANY ISSUES with any. So far with this car I have put about ,300 into it between repairs and a paint job because It had scratches all over it when I got it. I have been telling them to let me sell it from the day I got it but they wont let me and once again promise me to "wait untill I graduated College and they will buy any car I want" Ive herd that before. How do I convince them to let me sell it? or trade it in?