HOW DO I START MATURING?

I'm a senior in HS and about to graduate next week. I have been asking for a new car (camaro) for the last few months. I have done my research, created my goals and promises when i get it. I've worked with all of chevrolet dealerships around my area. It took a lot of work to convince my parents (especially my mom since she believes that im not responsible or mature enough to handle this type of car--she reasons that i've been in a car crash before & that it's a sports car & it makes her nervous). Last week i finally got her to come down to the dealership with the best deal and we worked on it and we were so close to getting the car but we came up short. She didnt get approved because she already has 2 cars under her name and we can't use my dad's. She wasnt willing to trade one of our cars (that was the deal breaker, they wanted another car to be traded in).. Since then, i haven't talked to anyone in my house and I've been pretty quiet. I also skipped school (senior ditch day). IDK. I just don't know how to act anymore. I've been pretty good (almost like an angel) when i was trying to convince them but now that I cant get the car, i just dont want to give a single f***. How am i suppose to act around them? Right now i just cant get over that car. I dont deal with disappointments very well. Any advice? Thanks