I'm going to repossess my ex's car
Is it really yours? Why would you repossess it?
I wanted to get even with her
You know what, sometimes I feel like people do not deserve what I have given to them, the same way that you're feeling right now. However you already have given car to them, and it's not in your possession anymore. If you really want it back, you should ask politely and if the person would agree then that is when you can take it back.
I'm not following what you're saying. I'm taking it back.
Okay, how about I put it this way? You gifted this car to your ex, so it's all in their name now and not yours anymore. I believe it would be wiser to leave your relationship as more friendly by not going through with this.