Read ALL of the documents you signed. More than likely you can be sued for breaching your contract. Without reading, no way for me to know. So, read the documents. In the future, read everything before signing.
Lucky for you that you reside in the Republic of Texas.
They can sue for breaching the contract.
You've already returned the car, and they accepted the return.
They can probably obtain a judgment.
But, in our Republic of Texas our constitution protects your stuff.
Your wages can't be attached, your home (if you are purchasing or already own one) can't be sold to satisfy the debt.
They have the car, and if they sue you, they'll have a pretty piece of legal paper that will be worthless.
Worthless, unless you win he lottery!!!!
So, relax, the only other harm they can do to you is ruin your credit.
I'd see that as a favor, because you can't dig yourself a deeper debt hole!
Debt, itself, is very evil and financially destructive.
Good luck.