My understanding is that it's not bad at all. The bad came from opening the account, and from here forward, the effect to your FICO score is exactly the same as if you had left it open, except that in seven years or so it drops off, thus shortening your AAoA and overall limits, at which point it will be as if you never opened it. So I wouldn't fret.
There's a great link posted under helpful threads at the top of the credit card board. "Closing Credit Cards" by Fused
It'll affect your utilization when you close it (but that's only if you carry balances).
It'll affect your Average Age of Accounts when it drops off your report (usually several yrs. down the line) - by then the AAofA is usually minimal.
I just closed a three month account that wasn't working for me. It's just fine.
I had gotten approved and did not activate the card because it was not the card I applied for but they reported it as open anyway. I canceled it right away and my score dropped 1 point.