Since OP had already purchased the liquor, he has little choice (unless he throws it away before departing), but to bring it through customs--declare it, and hope for the best [hiding it, as others have noted can have current AND future issues, if it is detected (undeclared).
A further comment, duty free (particularly liquor) is not the big bargain people believe it is. I've priced several items at DF in LHR, ZRH, CDG--they are NOT bargains. With proper searching on the internet, I've been able to buy some liquor at 1/2 the DF prices at those airports.
I can buy from an internet store (in the US) Courvoisier XO 750 ml for $99...