Trying to be a mature, responsible adult...but no matter what I do, it'll always be "just growing up"...

I decided after work to take my car into Firestone to have an inspection. $20, no problem. Two hours later, my valve gasket needs to be replaced. $800. I literally had to stop myself from having a panic attack. It's been a really crappy day on top of hoping to waste $20 to be told my car was perfectly fine. That $20 became $800, and it sucks. My parents told me to take care of the car, and that's what I'm doing.