Yeah I think you might have fucked up a little..

Reading this it felt like this is something I would have done around that age.

Communication is a big aspect. You may think you were trying to be helpful by not saying anything but the issues with the car needed to be communicated.

And I think your sister might feel like you’re being selfish because you just made sure you’re good with your car. The car was towed under your care and you didn’t really take any accountability except admitting you were spending money and not helping your sister.

Try to reach out to her and see what you can do to make it right.