I've been there, and done that Kim! Wal-Mart seems to be a favorite place for cretins to dump unwanted cats. Hope the female hasn't just had kittens! I've had to TNR (when I can) females that I get home, and then find out the next morning they're filled up with milk. I lucked out with one that I had to let go unspayed. Went back the next day, and found her nest of newborns! Trapped her again using the babies as bait. Hope she didn't get you too bad! Hot soak in Epsom salts if possible to draw out toxins.