Another puppy blues case here - I adopted a dog and now I don't know how I feel

Hi everyone. I feel like I need to vent right now, so reddit should be the best space, right?

Oh, well. Here we go.

I adopted a wonderful little pekingese mix. She's 2 y/o, healthy, and a street rescue. Somebody apparently abandoned her :( and let her to roam the streets. The local shelter took her in and that's how we matched.

She's a perfect dog. Quiet, playful, smart, and potty trained. She acts more like a cat than a dog. She has no typical pekingese traits like god complex, grumpiness, and aggressiveness.

Still, I feel overwhelmed. I have a pre-existing anxiety disorder which was in check for 3 years. But now I think it's flaring up again. I thought I did a good thing by saving this poor soul, but now the realisation "shit, I'm now responsible for this whole other life" hit me hard. I specifically sought after an adult dog from a shelter for this very reason. I had a dog as a child. A dog which grew up (and old) with me. I remember her from the day we brought her home as a tiny puppy to the moment the vet told me she's beyond help and had to be put down. That experience put me off having another dog for 15 years.

Now I can't sleep thinking I should've let someone else adopt her. She deserves better. Even if it meant her staying in the shelter longer. I'm also renting, which is not ideal. The flat owner is a nice enough dude and the flat is pet friendly with a pretty big terrace she enjoys but I still think I did her a disservice.