You think you did a good deed, but by using the power of Kreia's logic I shall prove you wrong.
First of all, according to you the kitty was trans-gendered. "Him" and "her" were both used when you described this kitty.
You gave this kitty to the PetsMart. I have never heard of this place, but the presence of the word "Mart" means that this kitty shall either be melted down to make gold, or shall be over-fed until it suffers a terrible fate.
Now, the ramifications of your deed:
This kitty might not've been stray and in fact lost its collar. The owners are desperately searching for it and by taking it away and giving it to a store of evil you have ensured that if the owners even did find the kitty (the chances of which are slim), they would have to spend a lot of money getting it back, effectively bankrupting them and resulting in them living on the streets in the worst parts of Detroit, Michigan (no matter where they actually come from).
However, if you had left the kitty to its fate it is likely the owners would reach it just as a gang of thugs came across it and attempted to destroy it. The owners would engage in a long, drawn-out battle, the wife would die and the husband would scream in agony at the sky. He would see the kitty as a dark omen, and shun it for eternity.
You have ruined everyone's life with your act, and if you had not committed it a similarly terrible fate would've befallen everyone. I hope you are proud of yourself.