Is AUTHOR wrong in the post ? POST : Throwaway because of personal info

A bit of backstory:

I’m 18 and I moved out of home when I was 16. I’m back temporarily because my university course was correspondence only for this term, and now that it’s over (it ended a week ago) I’m job hunting so I can move out again. I’ve been home for about 3 months and am likely going to be here for another two. I’ve paid my parents rent the entire time I’ve been here, every week on the dot, the exact amount they request. I also pay for my own food and rarely eat theirs unless it’s a dinner they’ve specifically made for everyone. 

My car is 100% mine. Even though I’m only 18 I purchased it with completely my own money that I earned from working full time. I pay all my own insurance and registration and gas. 

Now, I’ve often woken up at around 10am (it’s my uni break week, cut me some slack) to find my keys gone from my handbag and my car gone. My dad is usually the one who borrows it but my mum does occasionally too. They NEVER put gas money in and right now gas is about $1.60 AU per litre in my part of Australia (according to my math that’s $4.60 US per gallon). 

They rarely return my keys and I have to go looking for them myself. If I hide my keys, they get upset and make excuses that “your car has better aircon so it’s not hot” or “your car is safer in case of a crash” and “your car is better to put groceries in” as I have a large SUV while my mum has a small sedan and my dad has an uncovered ute. I’ve even been woken up at around 6 because my dad wants my keys to take my car to work. 

Why I don’t want them using my car:

My dad leaves my car a mess, and always changes my radio station and leaves the volume on max. I keep my car completely spotless as it’s a relatively newer car that I’m very proud of, and it pisses me off to get in and find used soda bottles on the ground and receipts everywhere. My mum is clean but she is an awful driver and her car is covered with dents and scratches from her hitting things. Both of their cars are perfectly usable, they just want to use mine because it’s newer and nicer. 

I feel obligated to let them use my car because they’re letting me live with them while I job search. Would I be the asshole if I straight up told them I don’t want them using my car? 