car.....

hey guys let me start off by saying that i am not selfish at all. My uncle sold me a car and i will start paying him till december because he said its okay to save money right now ! well i brought the car home and then my step dad started saying that hes gonna use the car whenever he needs it to work or go out, but he has his own car . i was mad because his car doesnt have any problems but he wants to take mine whenever he goes out.... am i wrong for being mad at this? my mom said the car is for the family whenever anyone needs it, but im the only one whos gonna pay for it sooo wtf..