If bought a service warranty at best buy on a TV about 5 years ago and then changed my mind the next day after I found it for much cheaper somewhere else. The store wouldn't refund my money (probably because he gave me a better deal on the TV if I bought the warranty)
However, I read the fine print in the terms and conditions of the warranty and I was able to convince Household Retail Services (BestBuy's Credit Card Company) to refund the money after sending them a letter and pointing out that I had the right to cancel the warranty.
If you paid via Credit Card, you may be able to weasel out of it by fighting it with the credit card company. Also, if you're a minor (under 18), I thought by law they have to return your money as legally you aren't old enough to enter into a contract.