Why does it always feel sucky doing the right thing?

I bought a dress from Nordstrom on my Nordstrom card and a few months later, I got the bill and paid for it in full. Anyways, I never wore the dress and returned it (with tags) and got a store credit on my card. Since I never used the store credit, Nordstrom sent me a check for the amount of the dress and I deposited it into my account. Three days later, I got another check from them for the same amount; they accidentally sent me two checks. So, being in a moral dilemma, I decided to call them to let them know that they sent me another check by mistake so, they voided it. I really wanted to keep the money but, I wouldn't have felt right about it. Talk about feeling tempted. Temptation sucks!!!!! I'm curious to know what everyone else would have done in my situation; I promise you, no judgements here....