Was GameStop going to give you $135 in-store credit or $135 cash? Usually if you take cash the TIV drops quite a bit and might make a difference for you. Unless you are going to turn around and buy "something else" at GameStop.
Personally, I would advise you just keep it. What does a new PS3 cost now, $200-250, right? +tax would be around $220-270. You've only had it a month and you're basically about to lose ~$100 to rent a PS3 for a month. To me, that doesn't make sense.
Edit: also, if it's just over a month old you should try returning it to whatever retailer you bought it from (assuming you kept the receipt). Even though it's my own advice I personally think that's kind of a f---'d up thing to do but it may be worth a shot and would give you all your money back.