If you bought it new and are having problems, there is no better solution than to take it back to the shop. Disassembling the chain, and fooling around with it after each ride, should not be necessary - and has likely reduced your chances of getting the shop to fix this at their own expense, which would be standard practice on a two-month old bike. (I mean, if you bought a new car, and the transmission wasn't shifting properly, would you tear it apart yourself, or take it to the dealer for warranty service?)