Will I regret my decision? Is it just puppy blues?

Please don’t judge me for this. I really just need advice.. I lost my soul dog who I raised since she was 8 weeks old in May, she was 12. I recently started missing having the companionship and all the joys that come with having a dog. After talking to my partner, we decided a foster to adopt trial may be good for us. He was not fully convinced but wanted me to be able to test it out. We spent a good week and a half looking for good matches because we have a dog savvy cat who loves to get close to dogs and he seemed to be getting lonely. We found a 1 year old pup who was found attacked by a bigger animal only a month beforehand. We decided to try to foster to adopt her. It’s nearly day 3 of having her and the GUILT and REGRET is eating away at me. She really is a great pup overall and ticks so many boxes off of what we were looking for. But my cat seems to dislike having her around. And I don’t feel the connection. I also don’t know if I’m fully ready. I really thought I was but now I don’t know. I’m an emotional wreck and don’t want to commit if I’m not 100% there. Does it get better at any point?